Coach Brittany posted her recommendations:
1st Year or ages 4-5
I recommend 4-6 hours per week and move to 9 hours by the end of that season or year.2nd–3rd Year or ages 6-7
A this age and/or level of experience I suggest training 9-12 hours at 3-4 days per week.3rd-4th Year or ages 7-8
I generally recommend 14-16 hours at a minimum of 4 times per week.4th-5th Year or ages 8-9.
In the 4th-5th year I would recommend 20 hours per week, training 5 days per week.
Those look a bit high for me. Especially in year one and two. We typically do 4 hours a week the year before Grade 1. Six hours a week in Grade 1.
On the other hand, I’m not worried for children of this age. They love the sport, improve rapidly and have relatively few injuries. This is the “easy and fun” stage of the sport.
Gymnastics Coaching.com 
Those hours are insane. At those ages kids should be doing a few activities not just gymnastics. We wonder why these kids break by the time they are 13. Most bodies and minds cannot handle that for year and years. I’d also say that 90% of my team and pre-team parents would just take their kids and do some other cheaper, easier sport.
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