There's the Wetlands centre at Barnes; you're not far from Chessington - rides are closed at this time of year but the zoo isn't and it's much cheaper when it's zoo only. You can walk into the miniature monkey enclosure, which is always a fantastic experience (if you love small monkeys wandering up to suss you out.)
Or you could go to Hobbledown Farm in Epsom, which is a children's adventure playground and farm with tractor rides, giant pillows, petting zoo etc. My DC could spend hours and hours there when they were smaller.
In Thames Ditton - so about 30 mins drive from you, there is a miniature steam railway club. They're only open occasionally but not expensive and 2 year old boys would love riding on all those tiny trains, looking at signal boxes etc. there's a really quaint old fashioned tea room there too.
Or take him to the pre-school section of the science museum - loads of water play and drums to bang (unless I'm out of date.)
Im bored. This weather is depressing, the beginning of my year was crappy my son got ill, my partner got ill, I got ill and at last we are all better. So we need to do something fun, something new, something that doesn't cost a fortune, just a day trip somewhere. My son is 2. I live near Wimbedon so any ideas would be fantastic. Please help????????????????????