Hello
I'm a Cardiff bod!
It's such a great city,
how long are you staying?
where are you staying?
what ages are your dcs?
then I can give you a more definitive answer.
Cardiff Bay is great, lots of restaurants and coffee shops to waste time in and on a sunny day great for a wander around. You can look at the Torchwood outdoor locations around the Wales Millenium Centre right in the Bay. Also in the bay Techniquest is good if you have little ones, good for any age 2 to about 14. There is a Dr. Who exhibition at the Red Dragon Centre in the Bay, also a cinema, bowling alley and restaurants there if it's rainy/cold.
If you like ice hockey or think it would be something fun for the children to go to, there might be a Cardiff Devils ice hockey game on. www.thecardiffdevils.com and there you would meet the wonderful me!
If you have any Tesco Days out vouchers you can use them on the sight seeing buses that go between the City Centre and the Bay.
Cardiff Castle is lovely as is Castell Coch on the outskirts of Cardiff.
The Museum of Wales (near city centre) is free and often has a good natural history exhibit plus an art gallery upstairs.
The Museum of Welsh Life 5 miles outside of Cardiff is also free and is a huge open air museum.
I can give lots more info if I know what your requirements are etc.
Cardiff is fab!!!