This is a tough one. In our house we have Little Touch Leap Pad, which would definitely be too young for your girls.
We also have a regular Leap Pad (a hand-me-down from our cousins) which is good, but a little too hard for Gregory still. Most of the books for the regular Leap Pad start at age 5 or 6, so Greg is just now starting to get any real use out of it.
We also have the Leapster and WE LOVE IT!!! Greg got it for his 4th birthday and could play and understand all the games right away. But, he tried one out last spring not long after he turned 3 and had a little harder time. He still enjoyed it, but it was definitely a bit challenging. Do you know anyone who has one? It would be great if you could let the girls try one out first to see how easy/hard it is for them.
We don't have My First Leap Pad (can you believe it, since we seem to have everything else this company makes). From what I hear it would be very appropriate for the girls 3rd birthday.
I don't know if that is very helpful or not. I do think that the Leap Frog products are very age specific. We seem to outgrow them and have to buy whole new systems around here. (Thus the MANY different products from them.) It works okay for us, since Greg has a little sister to pass them down to. I can also say that everything we have gotten from that company has been very popular with the kids. They never seem to get bored with the systems. And, as a teacher, I truly think they are indeed a great mix of educational and fun.
Let us know what you choose!