Kindergolf teachers follow a set of techinques taught to them so they are very basic and may not suit everyone. Some of the teachers may be golfers themselves, meaning already playing golf before joining them.
Depending what you want your kids to achieve, if just to have fun, go ahead and join, classes are conducted in groups so your kids can socialise.
If you want your kids to improve, I think 5 years old is good to engage a pro. their program is more suited to below 5 years old, depending on the maturity of your child