These people are maybe just trying to say that they are not bothered or offended even if DC do something a bit silly or impolite. It's kind human interaction to say "don't worry-it's ok!" if a small child bumps into you in a cafe, etc. - It is not necessarily said undermine you. Sure, there is safety to be considered, so, then even if someone says it's fine DC forgot themselves and ran into their path in the cafe, you still tell DC off and repeat to them that it can be dangerous, so you forbid running (or not being careful) in a cafe regardless, after/before you thank the other person for being understanding and forgiving on this occasion.
With food, I understand being super vigilant when DC has allergies etc., but otherwise, again, I think it is simply human, sociable and kind to want to share what treats you have with someone you like. I remember in my childhood being offered things by friends and, a few times, also boiled sweets or chocolate by grannies from their handbags, and it felt nice. Didn't make me obese or shun my dinner. Also, "sugar high" (from a finger of KitKat, nevertheless?) has been found out to be a myth.
Fine, I guess, also if you just prefer DC not to have anything at all between meals (even though I don't agree), but prepare DC for this food sharing situation (if it is that common to you and your lot). Then, if food is really pushed on DC, and the offering people will not take your or your DC's polite no as an answer (because they think you are just, again, trying to teach DC politeness and manners, or "stranger danger" and they do not see themselves as "strangers"), maybe just take the food and put it away in your bag for "later", then deal with any way you see fit.