I love grappling. Truth be told, I love striking, too. But when you hit someone, it's always going to hurt them. If you're grappling to work technique, no one gets hurt unless there's an unintended accident. Animal cubs can roll around with their siblings without hurting each other. If you don't already, you might try setting some guidelines each round, such as:
- 50% speed
- 10% strength
- agree to tap as soon as your partner gets into a dominant position, or secures a joint lock, or sinks in a choke -- so he doesn't have to actually crank it and risk causing injury
There are lots of games you can play, too, such as one person defending the whole round while the other tries to secure submissions, let them go immediately, and go for the next submission.
Just have fun -- play like puppies -- and keep in mind that grappling can be a lot safer than striking; you can eventually go with a lot of speed and strength, and as long as everyone uses control, no one gets hurt.