Teaching them how to throw the ball, or telling them how to do it (letting them do it on their own- like, “put your foot over here, grab there…”) or something like that? Go for it! I always love having dads at the park. I had one set of grandparents because I never knew my late father or his side of the family. I also had a big brother from Big Brother’s Big Sister’s of America.
My big brother was a middle aged man and now he is about to retire. I was born in 1984 but was raised more like a kid in the 1960’s.