For baseball/softball I have no problem bringing them up for JV games, but it's asking a lot for varsity games. Many schools have MS baseball and softball, which play in the mornings, so I suppose you could do both.
Our youngest was a decent left handed pitcher, and when he was in 8th grade, I went to the coaches and asked if he could practice with the JV/Varsity team, I didn't expect him to play much at all on the JV, but I wanted him to practice with them, his brother was a sophomore on the team. He was playing Babe Ruth and coaching was basically non existent. The coaches said they really didn't want him too, that it hadn't been done in years, but I finally told them his brother is playing, he can ride with him, I do not even care if you dress him JV, just let him come to practice.
They finally relented, the deal was Babe Ruth was the priority, and if games conflicted, he would go to BR. After a couple of weeks he was starting on the JV, the coaches were asking me if he could miss BR games, and I reminded them what our deal was, Babe Ruth was first, JV was just extra practice and playing time. They dressed him to have him on the bench for the varsity by the end of the season, he never played but it was good for him to see that level of play and pitching. It really helped him on his Babe Ruth team, he hammered the ball that season, and was one of the better players in the league.