Am I over paranoid? I notice my kids' childcare page have this Bangladesh guy liking photos of the kids. I clicked in to see his profile but notice he is not married & have no kids then why he is in the page? I don't know but I feel very uneasy

Bring it up to the school definitely. It's not wrong/illegal, but it is a worrying thing! But also you never know the full story, maybe he just doesn't upload his family background on Facebook? I agree with Harshit too, talk to your kid about strangers and make sure your kid is aware of what to do if he or she gets approached!