K.P.
I'm not a twin and I don't have twins, but the twins that I do know have always complained that growing up they got one present to share. I couldn't imagine if my sister and I had to share a birthday and share one present. I would get one for each girl. You can get them similar gifts, but different. Ex: different barbies or different each a different my little pony. I know a lot of people have suggested movies, so buy two different movies. The most important thing to the girls at such a young age is to have a present to open and something to call their own.