Hi sandra c,
I know very little about acorns, so I'm sorry to say I can't help much about that. I did read one reference here saying 3-7% acorns in the diet can be deadly to chickens
http://woodridge.wordpress.com/2010/10/07/acorns-toxic-feed-for-poultry/. However that's just one reference and it's not a science page.
But my feeling is acorns (unless absolutely tiny) wouldn't be an easy thing for young chickens to swallow. Are you sure they've eaten a number of them? Even if they had, I can't easily imagine the acorns killing so quickly. I could be wrong, and as I said I have no experience with acorns, that's just my general feeling (chickens are usually good at avoiding foods that disagree with them).
By far the most deadly and yet common illness at the ages you're speaking of would be coccidiosis. However you would probably have seen signs like hunching, ruffled feathers, pale faces, heads held close to breast, drooping wings and possibly blood in the droppings. Any or all of these symptoms can happen over time but it's worth noting that cocci can kill within 24 hours of first symptoms. Tractors don't guarantee safety from cocci.
Whatever the case, it's almost certainly time to move the tractor, perhaps try dosing with Sulmet or Corid (if you haven't already) just in case it's coccidiosis.
Sorry I can't help further, and ignore all this if someone wiser about acorns answers...
Best of luck, I hope you work this out,
Erica