Good place to break journey from Surrey to Cornwall?

[Smithagain]

We are driving to south west Cornwall on Saturday. We live in Surrey. I'm wondering if anyone can recommend a good place to spend an hour or two, about half way between those places.

I'd like to find something family-friendly but relaxing (i.e. the opposite of a service station!) Maybe somewhere we can have a picnic or a nice cafe lunch, then let our two girls be active for a bit. They are 4.5yrs and 21mo.

Are you NT members ? Seem to remember stopping off at Montacute House with ds. We're doing almost the same trip in the summer so will watch for alternatives

Thanks - might try that one. Have decided to set off at crack of dawn, so maybe we'll make it without a break, but it's nice to have something in reserve!