St.Fagans. It's on the border of cardiff it's an outdoor museum.
https://www.museumwales.ac.uk/en/stfagans/
It's free entry, just pay for parking, I think it's about £3.
My DH and I take LO there when we're bored.
Or Cosmeston Lakes.
Free entry again and parking is free, Just outside Cardiff.
https://www.valeofglamorgan.gov.uk/...s/cosmeston/cosmeston_lakes_country_park.aspx
There's loads to do/see around here.