I just ordered the iPad 9th generation last night for my 7 year old daughter but am now realizing that she can’t use the new Apple Pencil with it, which is why she wants a new ipad to begin with! Will the iPad Air 4th generation work with it and if what is the differences in the iPad Air vs 9th generation ipad? Is it just the size?
iPad
iPad9 supports the first generation Apple Pencil. By contrast, the iPad Air4 supports the second generation Pencil.
The two versions of Apple Pencil use a different pairing and charging interface - and are not interchangeable. Here is the definitive compatibility list for the Apple Pencil and iPad:
Apple Pencil compatibility - Apple Support
As to your final question, you can directly compare iPad models here:
iPad 9th generation vs iPad Air 4th generation
