Bradgate Country Park worked well for us on the way there - cafe for lunch and lots of open space for running around. Not too far from the M1 close to Leicester.
On the way back we had a bit of a longer break & visited Bolsover Castle. Bit further North but again not very far from the motorway. Lots to explore and green spaces for running around = lots of sleep in the car afterwards!
We're driving up tomorrow with dc 3 and 9 months. Where's good to stop for a short break for dc1 to have a run round and to have some lunch that isn't motorway services? Hopefully somewhere round Leicester close to M1. Any tips gratefully appreciated!