There's a great bowling alley at Cabildo 450, not far from where Santa Fe becomes Cabildo. It's called Poloko, and it's great for kids. Good coffee to boot!
In Caballito there is a mini-bowling place on Rojas and Gallardo called "new bowling". There's also Acatraz for "real" bowling on Rivadavia ( a few blocks down from Medrano). Have fun!