Fun adventures near SE London

[Twizbe]

DH is off on a 'baby stag' in a couple of weeks so I've got a weekend at home with the kids.

It's the weekend after our DD's birthday so I'd like to do a fun adventure with them.

I drive and we live in SE London. Kids are 5 and 3. Anyone got any ideas.

Happy to go up into town on the train or out into the country.

Thinking I might ask DH if I can take them somewhere with a hotel stay so could do a bit further.

Needs to be low cost or free activity as not hugely flush atm and if I do a hotel stay needs to be free activities. We're National Trust members and David Lloyd members so have those options for free too.

So any ideas?

Day trip to Brighton? The train journey is an exciting adventure in itself for kids that age (under 5s are free, and I think over 5 kids only a couple of quid with an adult ticket).

I did think about Brighton as it's an easy train ride for us. Any tips for places to visit there?