Should have clarified: "Red routes" are proper cycle paths, they are completely separate from the roads - good for all ages to walk and cycle away from traffic. You don't really see people walking along the main roads there.
And Woburn Abbey has a big safari park that you can drive round.
From memory, you can get season tickets for Bletchley Park and Woburn and may be one on two other places, so you can use it all year.
Forgot to mention there's a fairly decent theatre. Also an art gallery.
On heritage days every year for about a week in Sept, if you have an Milton Keynes postcode, you can get free entry to the Museum, Bletchley park, MK Gallery, plus other events.
There are other events now and again such as the Dragon Boat festival.
If you like the outdoors, the Parks Trust put on regular family-friendly events, obviously in one of their parks.
Also, Salcey Forest and Emberton Country Park are both only a few miles north - both are very good for walks, bike-rides, picnics, play park and both have a little cafe. You can also barbecue at Emberton (it's quite common to see people having an outdoor get there in the summer)
Olney is a little market town beside Emberton Country Park and has some nice little independent shops, cafes and pubs.
Lots of other little villages with nice pubs and gardens.
It's actually a really good area for families.
I've never really written it all down before but now that I have I feel I could apply for a job at at their tourist board😂
Anyway, good luck with your decision!