Need Birthday Present Ideas for 3 y/o twins and 1 year old

DHs cousins are having a combined birthday party...so three gifts to buy Or could I buy ONE gift for all three of them? I guess I want to spend $30-$50 dollars total. Oh...and they're all boys. They have a huge backyard with a pool if it matters. i do not know them personally that well as we only see them on family occassions so I do not know what they have. Is a $50 TRU gift card for all three ok? Its amazing how I never seemd to have a problem picking out baby toys BEFORE I had one