This question is as age-old as “how long will it take my child to get good?” If only the answer were as simple as asking the question.. Here are a few guidelines to help you know what is best for you or your child. If the child is under the age of 5 you should expect no more than 5 or 10 minutes of practice at a time. It is a victory at this age to get in 3 days per week. Around ages 6-8 you should expect no more than 30 minutes of practice per session, ideally accomplishing that 5 times per week. By the age of 9 or 10 a child is capable of longer periods of practice and daily can be expected.
Having said that, PLEASE understand each child is different and learns at a different pace. If you have a child who is 9 years old and can’t focus on practicing for more than 15 minutes at a time but is still eager to learn and loves having lessons, threats to stop the lessons if the practicing is not daily for an hour at a time will only be a huge wet blanket on their excitement and quitting will wind up looking like the only option to the child. If your child is young and can practice for an extended period of time, count your blessings, encourage your little Mozart and reward their efforts.
As much as we like to think our kids are all musical geniuses, the simple truth is that if they will keep plugging away at their pace they will learn. The goal here is enjoyment, a feeling of accomplishment which increases self-esteem and of course all the other named and unnamed benefits music can bring. Most of all have fun!