It’s a shame that this is the first suspicion of most people when an adult male offers child care, but so it is.
When I was in high school - and I wish I could recall the context as to why my dad had to bring this up - my dad told me that normal men do not like to watch children, babysit, and all of that. Men just aren’t wired that way. He was ALWAYS suspect of any adult man who wanted to be around little children. And, he was right. About a lot of things, I might add.