My boy is 3 and 4 months. He has very little interest in any kind of technical grappling at the moment )he just likes general wrestling on the floor with no technique!), but he is a big fan of punching, kicking and now knees. The rules are that he has to say he wants to fight first before he does it, so that he doesn't just start swinging at people (particularly his mother!). Generally though we have to have a gun fight first, then we have a sword fight, and then we go to fisticuffs. He also likes to go 'slo-mo' and watch me make funny faces as he throws slow motion horrible Wanderlei Silva hooks at me.
I've tried playing some grappling with him, but I think it will be easier when he has someone his own size to work with. I'm going to give it a little while longer and then see if I can find him some Judo locally.
Sorry about late reply but she really loves grappling I could not ask for her to be more enthusiastic towards it. Well either She loves it or just enjoys attacking Daddy lol. (Shrugs)