When purchasing or renting instruments always get a quality instrument that suits your child. String instruments (guitar, violin, viola, cello) should be properly sized by a professional. Be cautious when ordering instruments online. It is always best to test an instrument prior to purchasing.
I recommend purchasing or renting instruments locally if possible. Below are reliable vendors I have used in the past and they provide good products and service.
26469 Center Ridge Rd.
Westlake, OH 44145
Sweetwater Sound Inc.
Facebook Marketplace is great for purchasing used instruments/equipment.