Talk

Ikea?

you could go here

just off junction 17

There's also all these at Cribbs Causeway off J 17

www.nationaltrust.org.uk/main/w-vh/w-visits/w-findaplace/w-stourhead/

Stourhead near Longleat just off the A303 is really nice - nice cafe, lots of open space for small people but you'd have to check out
disabled access for the open areas.....
Might be a bit out of your way but thought I'd mention it !

Try Brewsters in Portishead, just off J19, as you go ino Portishead.

It has a giant soft play area, and outside play area, food is ok, nothing amazing, but they have a reasonable kids menu.

here

There is a cafe/bistro at Ashton Court if it is dry (the cafe is indoors but your DC could burn off steam outdoors). 10 mins from the motorway.

There is a Pizza Express in Clifton village, again 10 mins from motorway, which is very child friendly. Park on the Leigh Woods side of the bridge as loads of free parking, walk over the suspension bridge (there is a play park on the left on the Clifton side) and PE is a 5 minute walk.

No 5 The Beach in Clevedon is child friendly too. There is a park on the sea front, a walk on the pier which has a tea room at the end.

thanks all-I think i might go with Ashton Court Jx