Generally get what you paid out of them or more. You’ll likely start with an 1/8th size and go from there. Now is the time to start your child if they have the interest. My youngest has been playing cello since the age of 4 and is better than most college cellists that are going to school for cello performance (her teacher is a major college cello professor and has her do solo performances with the college students she taught). She already has a couple of college offers with scholarships. So it can turn into something bigger.