Split flipper can be fun! When I play with my nearly three year old daughter, she either mans the plunger or one of the flippers. As the more experienced player, I do my best to keep the ball alive on my side while she flips with absolutely no regard for what's going on. It's great though, she loves it and I get a kick out of her narrating the playfield. She gets very upset about the trapped ball!
The thing that annoys me is when somebody who has no money in a machine is hunched over the machine, playing the flippers anyway. At an arcade in Jersey there was a kid around 7 doing that at the Dark Knight table, which I was very excited to play. He was there for like at least a minute with me standing behind him. As kind of a gentle hint, I put my quarter up. Kid took my quarter and put it in the machine! I then had to explain to him that putting a quarter on a machine meant that somebody else wanted to play when you were done, and he kind of sheepishly ran away. Came back while I was playing, though -- it's obvious he hadn't seen a lot of pinball games.