Kids are weird as hell, and it's up to parents to lovingly guide them away from creeping everyone else out with their unbridled curiosity. It's completely normal for children to ask invasive questions about body parts, it's also par for the course for them to occasionally grab you in ways that would warrant an HR complaint if they were grown.
However, in these situations, it's generally the parents' role to gently let them know that groping isn't okay, and they should probably get your foot out of their mouth unless they want to get sick. When parents don't set these boundaries early on, it can set a child up for very awkward run-ins at school and potential trouble.