I envy you: I have never been to Shiloh NMP, but hope -- one day -- to make the visit. [In the meantime, I have concocted a Route that I would follow, if I had the opportunity to take family members, so they would get an appreciation for the vast expanse of Shiloh Park.]
During the drive up, I would provide details of the units we were going to focus on (in my case, five family members of the 12th Iowa Infantry, Co.H). I would bring pictures, stories, make them "as real and alive" as possible. (Your ability to "dress in costume" and have other props, is good idea.)
On arrival: my focus changes. "Here we are, at Pittsburg Landing. A big expanse of woodland, cut by a few isolated farms. And it was just a big camp ground, from here, all the way to the river: both sides of the road. Big, white canvass tents, each one holding ten men; over 3000 tents scattered in small clusters, from here, to the river: it looks like a circus, or carnival, but on a grand scale. Men can be seen marching; some are playing baseball; on rainy days, they stay in their tents and write letters, play cribbage or euchre or chess. And there were not just men here: some of the men brought their wives. And, there were wagons full of supplies, and food and ammunition; there were big artillery pieces -- (just point at any random gun you happen to pass) -- and there were horses... four horses to pull each wagon; 12 horses to pull each gun. And all the senior officers rode horses; and hundreds of cavalrymen rode horses... Hundreds of horses, perhaps thousands of horses, here to service over 35,000 men."
First stop: the bluff overlooking the Tennessee River (ignore the visitor center until the end.) "The men who setup their tents in that camp ground we've just driven across arrived by boat, from over 200 miles away, in that direction (north). In early April 1862, there were a dozen steamboats here, every day: some coming, some going, a few that stayed (one for each of the five Union divisions here, and these acted as "floating warehouses," full of ammunition, supplies and food.) Also on the river was the U.S. Navy: two, and sometimes three, armored steamers, bristling with guns. Here to protect the steamers full of men making the voyage from St. Louis and Cairo and Paducah. Up that way, to the north, is where General Grant, commander of the Federal Army here, had his headquarters: Savannah, about eight miles away. Also five or six miles away was another camp of Federal soldiers, at Crump's Landing. Lew Wallace and his division of 7000 troops (you may have heard of Lew Wallace, and how he got lost. We can talk more about that, later.) Across the river, another big Union Army, belonging to Don Carlos Buell, was marching over 130 miles from Nashville, along mud-affected roads, and delayed by burned bridges that had to be rebuilt. That eastern bank of the Tennessee River was a swamp in 1862, five miles wide. Buell's Army had to wade through that swamp, to get to steamers; climb aboard those steamers and ferry across... to here, the Landing, just below the bluff. And, once Buell joined his 30,000 soldiers to Grant's 35,000 soldiers, they were all going to march 20 miles that way. southwest to Corinth Mississippi, and engage the Confederate Army commanded by Albert Sidney Johnston and PGT Beauregard. And they expected to fight the battle -- there, at Corinth -- that would end the War in the West."
Still near the first stop, but if possible, reveal the Dill Branch Ravine. What can be said, about this ground we are standing on? [High... elevated... can see for miles (when the trees don't block your view)... and this Dill Branch Ravine (and another one, not quite as deep, called Tilghman Branch, just off to the west)... All of these features made this Bluff a strong position. If the Confederate Army was going to win the Battle of Shiloh on April 6th, they had to knock the Union Army off this bluff (and the Rebel plan was to push the Federal soldiers west, into swampy ground adjacent to Owl Creek and Snake Creek, and destroy the Union army, there.)
On the drive: if possible, drive slowly to reveal the extent of Grant's Last Line (and explain "this came later," and point out Tilghman Branch Ravine.) Perhaps indicate the general directions that the five Union division commanders had their camps, as you proceed "to where it all began," Fraley Field.
Fraley Field: the first shots of Battle of Shiloh occurred here, pre-dawn April 6th 1862. The Confederate Army had camped just a mile or two to the south -- most without tents, and most went to bed April 5th hungry, having run out of food during the march from Corinth. Albert Sidney Johnston had planned to launch his attack on April 5th, but nuisance rain made the road muddy. And soldiers had to help push and pull wagons and artillery pieces through the muddy bottoms, through waist-deep mud. The plan: Johnston (and Beauregard) wanted to attack Grant's Army before Don Carlos Buell completed his march from Nashville (because it is a lot easier to defeat a force of 35,000 green troops, than it is to defeat an army of 65.000). And the size of the Confederate Army is estimated at 35,000 men. And they hoped that by fighting on their ground, familiar to many; and by taking Grant's Army by surprise, they could overwhelm and Defeat Grant's Army. And then confront Buell (possibly run him back to Nashville.)
But, here at Fraley Field, it came unstuck. An unsuspected patrol sent out by Colonel Peabody, 25th Missouri (now acting as Brigade Commander in General Prentiss's Sixth Division) had encountered Rebel troops, and the fight was on... while General A.S. Johnston was still in process of readying his men to make their attack. The Federals under Peabody and Moore and Prentiss, believed they were just engaging a Rebel Patrol, not the whole Confederate Army. So as A.S. Johnston completed his preparations, and sent his Army forward, the Federals added more and more troops from the Sixth Division... but 4000 Federals were never going to defeat an Army of 35,000. Peabody was killed; and Prentiss was pushed away to the north... but before he left the vicinity of his Camp, General Prentiss did the most important thing he could have done: he asked for help. He sent a messenger north to General Hurlbut, to ask for help from his Fourth Division; and he sent a messenger, asking for help from the Second Division; and he let Colonel Stuart know (Stuart was in command of a Brigade belonging to Sherman, away to the East, on the left side of Prentiss's Camp). Prentiss sent a messenger to tell Stuart that he was under attack. So, what do we see? The surprise that General Johnston was hoping for evaporated pretty quickly."
Now, drive to Cloud Field, and continue your lesson. And follow your "Regiment of interest" in its moves during the course of the day.
Finish: if following a Confederate regiment, end on the south side of Dill Branch Ravine (or west side of Tilghman Branch Ravine). Because these natural barriers, with Federal troops lined along the north of Dill and east of Tilghman, are what the Rebel soldiers had to overcome to win the Battle.
Finish: if following a Union regiment, end on the north side of Dill Branch (or east of Tilghman Branch, where Sherman had his Final Line aligned north/south, protecting Snake Creek Bridge).
Visitor Centre: now go inside, view the movie, have a look at artifacts and buy souvenirs. (By conducting your tour in this order, the movie is used to reinforce what you explained during course of your lesson.)
More than happy to answer any questions...