You may be the most gluten-conscious person in the world, but there's still a chance that gluten will enter your gluten-free child's diet. Not to worry. Gluten is not poison. It may temporarily cause some discomfort, or diarrhea or some of your original symptoms when gluten was regularly in your child's diet. But a minimal exposure when something slips is likely to be quickly repaired when the gluten source is removed.
If that sounds too vague for you, that's because different people have different levels where gluten will upset their systems. In essence, some people are more sensitive than others. Understand that even gluten-free products can have tiny, tiny amounts of gluten (up to about 10 mg per pound of bread, for example). Since researchers estimate that it takes about 10 mg to do any intestinal damage, your child would have to eat an entire pound of that bread to notice any symptoms. On the other hand, regular bread contains much larger amounts and a single slice might cause symptoms that last for several days.
But the intestine is a forgiving organ, with some of the most rapidly growing tissues in the body, and constantly repairing itself. So minimal, infrequent exposure is unlikely to cause long-term problems, though it may cause short-term symptoms. On the other hand, repeated exposure does have the potential to cause more severe symptoms and the consequences that we try to avoid by treating celiac disease and non celiac gluten sensitivity in the first place.
Do try to be thoughtful in how you present this to your children and others. I do recall a parent telling me she had tried to steer her son away from gluten by telling him that gluten and wheat were poison. Of course, that backfired when she took her son into the grocery and he was screaming as they went through the bread and cereal aisles, wanting to leave immediately because of all the poison surrounding him.