Well both the cellos and the violins should come in different sizes like 1/2, 3/4, 4/4. If your school is not having a sizing try the instruments out day, then I would find out who is renting out the instruments. You could always go directly to the strings shop and try out both and violin and a cello and get sized on both.
Our local strings shop is really friendly and has an awesome rent to own program that I would imagine is pretty universal. The monthly rental fee goes 100% towards owning the instrument. When the instrument gets too small, you can trade it in for a bigger one. Bigger and better instruments cost more, but you don't lose any money to swap up. My point is, you child should have an instrument that fits, whether it is a violin or a cello.
We are a violin family, but dd is curious about cello because then she could practice sitting down all the time. (At school she can sit with her violin, but at home and in private lessons she has to stand up. Life is hard...)
Long arms and fingers are good for violins too.
Bigger violins cost more than little violins, so I would guess that cellos cost more than violins. But that is only a guess.
At our school, there are more violin players than cellos, basses or violas. So picking something other than violin might highlight your child more. But then again, if you are ever looking for a private teacher, there are tons more violin teachers out there.
Best.
