A nice childrens book is good idea.
If you dont know what to get, give a donation to childrens charity in their honor. Charity donations amounts are kept secret to receiver, all they know is donation was made to that charity.

I love gift cards (giving/receiving). When I give one, I pick a store/resturant etc that the person loves to shop or eat. It's the thought that counts NOT the amount I'm giving. Normally that amount will "help" towards the meal or shopping experience.
When I get one, I love it. Normally it's my favorite store "Michaels Craft Store" and I can get all sorts of things for $20 dollar gift card or less. Sometimes it goes towards 1 item that I might want to get or a bunch of stuff on clearance.