My 5yo niece knows exactly what she can and cannot eat due to her allergies.

Ditto with me around that age. I chose to become a vegetarian at around 5 or 6. I knew what meat was, and I steered clear of it by choice. As some have said, I wonder if Alex was even aware he was supposed to be vegetarian. My only concern is; how long has Alex been vegetarian? If it's been a long time, eating meat could potentially make him sick. That said, if he was fine eating dinner there, and then sleeping over, maybe he was okay?

My kids' dad is non-dairy and our daughter was making sure things were 'daddy safe' when she was 3.

Halal food indicates a possible Muslim family which means that pork and sweet potatoes are off the menu as they are seen as unclean in that religion. Also, the mixing of milk and meat during cooking in Jewish faith is strictly forbidden.

Speaking as a Muslim that was very irresponsible of you. Kids are still being taught religious rights and wrongs and certain boundaries pertaining to their religion. They are not always to going to follow the rules of that religion, just like all kids who test limits and see what they can and can't get away with. If course kids are going to gravitate towards something they are told not to do. As the adult it was your responsibility to inform the parents who entrusted you with their kids what they were eating. Everyone on here that says a 10 yr old is old enough to know what he should and shouldn't eat seems to forget that a 10 yr old also likes to choose what they can't do more than what they can. If a parent tells you something about their kids diet while they are in your care you have taken that responsibility to respect the parent's wishes. At the very least inform the parent of what happened. Nobody cares about parent's wishes for how they want to raise their kids anymore.