My son did it when he was older, both teams in same program. I don't recommend it. He would get called up for the older team but didn't always get playing time. Got old. I would think of it more in terms of how many days a week a kid plays baseball. Plus, practice is important, especially before high school. I'm not sure kids that age absorb teaching during games as well as they do in practice.
My son and I recently talked about a friend of his who is playing on two teams, and he thought is was a bad idea.
Before graduating from high school most serious position players will play in hundreds of games without playing on 2 teams at once. It is a marathon!