I agree to a day out, I see your on the central coast, have you been to the reptile park? lots of fun for small boys.

My nephews are the same as your DS's both have oodles of stuff. My mum gave them a myfun pass and they could chose where they went. I think they ended up going to the aquarium, the Australian zoo in the city and one other place which for the life of me I cannot think of. These places all have take a photo with animals kind of places which could be a good birthday/ Christmas momento?

While vouchers are not that great for someone so little, perhaps a big card with all the adventures they could choose and get them to pick the ones they want?