Absolutely not pushing. If they love it then give them more! That kind of self-motivation is exactly what you want to nurture.
I'm not sure what's out there now, but I know there were some great computer games for kids that were math focused in the late 90's. If you see any at thrift stores or a half price book they're generally pretty good. Everything is read out loud so there's no big problem with kids that don't read as well as they compute.