Can your child's teacher not advise? (It's part of their job) They may even be able to help you buy one - trying it out, checking it etc - (not part of their job, but many are happy to do it)

If not, contact your nearest LEA instrumental teaching service - they will be experienced in buying instruments and may even be able to put you in touch with a dealer where you can buy one at preferential rates. Many are happy to check instruments too.

Cheers