My personal view is that for children and adolescents lifting weights is very important for strength, bone density, coordination and self confidence.
I feel less than 10 repetitions is unnecessary and counterproductive since the majority of (kids) that are lifting are for a sport that involves massive amounts of repetition to properly learn the movement, just like weight training.
If the weight is too heavy to reach 10 repetitions, then less weight should be used to aim for 10 to 15 repetitions.
Proper form should be stressed more than weight amount when dealing with children as well. The better their form becomes, the stronger their core muscles grow, and the more weight they will be able to lift as they grow older.
It takes 3,000 to 5,000 proper repetitions of a movement for it to be ingrained into muscle memory.
Starting with a slightly higher repetition max as a kid only puts people ahead of the game for when they are working out as a teen or adult.