What if people who have children approach them differently from those without, and it's noticeable?

Before my male friends had kids, they were tense and apprehensive around toddlers. They worried they would hurt them, etc.

Now, they act like Dads, even with kids who have nothing to do with them.

These guys weren't bad people to begin with. They just didn't radiate "dad energy" for lack of a better phrase.