I don't think that's a good idea ... We have to let young horses growing in a good way without our intervention :)
I know it is not very recommended... It can have bad consequences on the horse's back and legs later.
It is a good way to analyze the horse's jumping capacities but be sure the line before the obstacle is well adjusted so that the foal jumps with the right stride.
But I agree with Tessy, do not do this too much, the foal is still growing and his body is not as strong as the one of a 6 years-old horse.
If the horse is less than 4, it is not really recommenced. I absolutely understand people want to see how their horse jump and it is not a problem to make him jump free sometimes but it must stay very occasional!
Under 4, the body is not fully-developed.