Disclaimer: I am not a doctor. If you are seriously worried about your child talk to your doctor. Celiac symptoms may vary, this is just my personal experience and I hope you find it helpful.
My son was two when he was diagnosed with celiac disease. If you have any experience with two-year-olds then you probably know that they are not the easiest to communicate with. Does “I warregert” mean “I want water” or “I want to go” is he crying because his tummy hurts or because he can’t find his toy? Distinguishing from when he was being a normal kid and when he wasn’t doing well because we’d had a gluten mishap was HARD. After a couple of years of talking to doctors, reading, and his communication improving I’ve figured out some basic signs that he’s eaten gluten.
One of the most immediate signs is drowsiness. 20 minutes to an hour after a meal the guy gets glossy eyed and just wants to lay around.
The dude also gets grumpy. This one can be a little trickier since kids aren’t happy 100 percent of the time, but if an hour or two after he’s eaten my little guy is sleepy and horribly crabby, and there’s no other obvious cause, I will go back and double check what he ate last to see if it contained gluten.
The last, and the most obvious sign that he ate something containing gluten is tummy troubles, like diarrhea, constipation, and gas. In his case this isn’t noticeable until later in the evening or the next day after eating gluten. This one is always a sure sign he ate gluten.
I’ll also add that the longer he goes without gluten, the more obvious these signs become. Knowing these signs has helped so much in making sure he’s not eating gluten.