I have both the LeapPad Ultra and the LeapPad 2 and the cartridges will work in both. Also, even though it says 4-9 on the package, you can set up the child profiles as young as early Pre-K up to a 6th grade level. I am a kindergarten teacher and have used LeapPads in my classroom and plan on using them when I move to a 4th grade classroom, too. The learning apps adjust according to whichever level you set up. For example, the Pet Pad Party game practices letters and numbers at the K level, but multiplication at the 4th grade level.
I hope that answers your question!
Yes, the LeapPad 2 games will work on the Ultra.