It's unusually hot here at the moment, high 20's but hopefully next week will be cooler.
For the whole family, I'd go to the Aqua Park, it has some cool slides and pools and would be more interesting than the ordinary baths for kids.
If you like history, the Hospital in the rock is worth a visit (
https://www.sziklakorhaz.eu/en/), but not really for kids. There's also the House of terror (
http://www.terrorhaza.hu/en/museum/first_page.html), but I personally think that's overrated.
Apart from that, it's a nice town to stroll around. Restaurants can be a bit hit and miss though. If you fancy going out of town, there's a bear park about 30km out of town (
http://medveotthon.hu/). Depending on the kids ages, they should enjoy it.
Depending on when you're coming, check out if there's any festivals. One of the things I really enjoy about it here, is having a cold beer outdoors at one of those things. There's a couple of beer and wine festivals throughout the summer, so if there's one running while you're here, you should check it out (and they're surprisingly kid friendly).