London to Cornwall - great places to take a driving break (new baby & 3 y.o.)

[MayfairMummy]

Looking to head to Cornwall for a few days to celebrate one of those awful birthdays with an 0 at the end .... driving with a newborn and a very active 3 year old. Any suggestions for places to break the journey to make it an easier trip? TIA.

Lydiard Park near Swindon - 5/10 mins signed off junction 16 M4. Brilliant playground and lovely grounds for picnic. Small cafe. Free
Knightshayes Court - National Trust near Tiverton - 10 mins or so from M5 junction 27. You can just use cafe and go in woods for free otherwise it costs unless you are members.
Also Darts farm near Exeter - farm shop and more - I think playground, but farm stuff too and I think somewhere to picnic. Never stopped at this one but warmly recommended by friends

Depends how far down cornwall you are going. Bristol is a good one @bristol musuem is brilliant for active 3 year old lots to see and do and buttons to push or the ss Great Britain if he likes boats. Plymouth is another good stopping point if going right down the end. assume you have already booked something if it is for this weekend/week as it is half term and cornwall seems rammed at the moment. where are you going to?