I'm thinking of asking an older man to leave the skatepark my kids were at and then threatening to call the police when he didn't
Why does he need to leave, it is a public place?
He's not from my culture and it's the skatepark my kids play at.
Well, the skate park is a public place meant for everyone. You can't tell people what to do nor can you just go around calling the police for no reason. The world is a big place, and you should embrace all cultures.
I won't allow people from diffrent cultures to come to my country and ruin things.
That sounds pretty harsh, I think that it would be best for you to just mind your own business. If he is not bothering anyone there is no reason for you to tell him to leave.