Hi there - do you have a wooden fence at all? Just thinking you could give the kids a small container of water and a paintbrusha and they could paint the fence with water. Playdough is good too - although you'd have to watch them closely - Playdough is tasty!!!!(apparently)
with regards to a present - What about one of those Little trikes cars. My dd3 got given a hand me down one and she loves it! She can only go backwards in it at the moment, but she'll go forward soon!
Trampoline's are great too - the enclosed ones though. You can get toddler sizes ones - that are cheaper than the big ones.
The sandpit can be messy, but my youngest dd loves it (the bigger girls do too) We have one of the shell ones, so you can cover it up when you don't want them to play in it.

Good luck. I hope you find something.