No wonder my 13 month old didn't sleep well last night; this morning it looks like he's broken out in hives. At least, that's what I think this is because I've never seen hives before, but they look like various sized welts on his check and all over his thighs and tummy.
He's perfectly content now, but I imagine they were bothering him last night as they were appearing.
I'm assuming I give him some Benadryl, right? How much? I just have Children's Benadryl.
Is there something else I should do? Change his clothes, bathe him, change his sheets, etc?

Re: 13 month old has hives, How much benadryl?
Depends on how much he weighs. My son weighs 23 lbs and we were instructed to give him 3/4 tsp of children's benedryl. I'd call the pedi.
When my DS broke out into hives they advised no benadryl.
To clarify, by 'they' I mean his pediatricians.
Your pharmacist can tell you if your doc is not available.