Where do Forest Hill-ers rate for this? Preferably no more than an hour or so - two small children to entertain. Not Leeds Castle - been there, done that...

I'v recently moved to the area and am looking for places too! One place we went to was Hall Place near Bexley Heath which is less than an hours drive away.
http://www.bexleyheritagetrust.org.uk/hallplace/

free to get in to the grounds and they often have activities for kids.

Brighton is not much more than an hour away. Camber Sands takes a little longer, but actually has sand (nothing else, but sand nevertheless).
Kent is full of nice spots to go. My recommendations are:
Down House which is in a nice little village with Charles Darwin's House.
High Rock for a nice walk with surprising rock formations and a steam railway running past the pub.
Closer to home are Chislehurst Caves which are another geological surprise so close to London.
And there are lots of nice woods: Petts Wood, Keston Ponds, and Sydenham Woods.

Thanks for the tips Shimmysister and Michael. Plenty to try out there already!

I stumbled across this pace last summer while cycling one Sunday
; http://www.shoreham-aircraft-museum.co.uk/teas.htm

Quite an extraordinary experience, akin to Brigadoon in the timelessness of the local inhabitants. I really had no idea that such communities existed not an hour's drive from SE London. Well worth a visit on a bright sunny day as the countryside's quite stunning, but Shoreham may appear just once every hundred years or so......

There is also Chartwell House, Rochester Castle and the superb National Fruit collection at Brogdale which also has a miniature railway.

Eltham Palace is lovely - an art deco house added to an old castle, plus loely gardens. Less than an hour away.

Whitstable for some oysters and a stroll down the high street.
Godstone Farm - more than just a petting farm
British Wildlife Centre - further down the A22
The Pinetum at Bedgebury - fantastic walking or hire a bike with the kids
Bluebell Railway

Think most of the other posts cover it. Our eldest is now 6 and we have a 2-yr old too, so have explored A LOT of options!

The National Trust and English Heritage websites (and apps) are pretty good for acquiring targets and finding out about special events.

Some favourites are:
- Knowle Park in Sevenoaks
- Ightham Mote nearby
- Chartwell near Westerham
- The Bluebell and Kent & East Sussex Railways
- Bedgebury
- Camber Sands, Winchelsea, Rye and Hastings
- Sheffield Park - handily close to the Bluebell Railway
- Box Hill
- RHS gardens at Wisley - and the various theme parks nearby - Thorpe Park etc.

Basically any bit of the North Downs, Kent and Sussex accessible via Bromley, Biggin Hill and Westerham (which I think is the most civilised way out into the country from Forest Hill) or for an early morning jaunt the A23, M23, M20 and even the M3 and 4. Lots to do...!

Brighton is highly recommended as there is so much to do. However, go by train as the traffic as the weekend can be terrible - can take up to two hours on busy Saturdays/Sundays. However, if you did go at the weekend and got stuck in traffic, you could change your plans and go to the Blue bell Railway at Sheffield Park.
Or if you want a really short drive, why not go for a walk in the woods at Beckenham Place Park?

There is also the Royal Military Canal which runs down to Hythe. As does the Romney, Hythe & Dymchurch railway. All great for family walks, picnics and cycling. Mostly flat as the canal was for defence purposes.

oops, posted to wrong thread. Sorry!

I can recommend Ightham Mote but more for the lovely country walks around the perimeter as much as the gardens which is free. Close by is the village of Stone Street with some great pubs including the Snail- great for Sunday lunch!

Whitstible is fantastic.

The best place to visit for a walk, and which is only 40min from Brockley Rise is somewhere I am pleased to say isn't on your lists