I like the idea a lot. Its really cute and 7 to 8 year olds love horses. But my only critique is to maybe make some of the sentences a little bit more simple. There very good, but just sort of difficult for a young kid.
And also, when a different person speaks, you just start a new paragraph. That may be from copy and paste (it happens to me), but just fix it. Its a common mistake
Anyway, It's a really cute idea and I like it a lot!