Depends on ages.
Techniquest is fab, they do a year pass which works out far cheaper.
There is a great pirate sandpit doen at the Penarth side of the Barage (need a good weather day for this!)
Roath Park Lake
Community Centres such as Plasnewydd off city Road do toddler groups that run in holiday time with bouncy castles and soft play.
Museum & castle
Ride an open top bus
Hope that helps
Thanks Frankie. I was looking for something to replace Tumbletots type things, and have found something if anybody else is interested. Spotted an A board on Albany Road advertising kids classes in ballet, kickboxing and boxercise at Dave's Gym. 3- 16 yrs. I went in and asked and they seem like a good idea. They start from the 24th. If anybody else is interested, you can call them on 2046 0232. Am planning on taking mine down there and getting somebody else to knacker them out for me!!
If you've got a car I'd go to: St Fagans - free to get in, only have to pay for parking. Margam Park - again, free to get in but you pay for parking Both are a fab day out which won't break the bank if you take a picnic, have playgrounds to wear them out and often have extra activities/events on in the summer. Both also have a farm area so you get to see pigs etc.
Cardiff Castle is free if you live or work in Cardiff.
The Museum is free and great for a wet day.
There are often lots of things going on in the Bay during the Summer Festival period - take a boat trip, go to the park...
Swimming if it's raining wears kids out, feels like a day out but won't break the bank either - the International Pool in the Bay with all its slides and things whiles away the hours.
Check out Penarth summer pirate themed festival week of activity ending with fireworks at the Pier.
poo2 I just went in to Dave's Gym and asked about that and they looked at me like I was mad . Was it definitely thereor another gym? Or maybe I got a member of staff at the desk who knew nothing about their programmes and who clearly thought kids' activities was a mad idea