I just can't even fathom that a 6yo level 4 has plateaued - and is training 12 hours a week.
There is a lot that can be accomplished in 12 hours. If they are telling you that your child has plateaued, they aren't being honest. It's impossible - gymnastics is a progressive sport and one skill leads to the next...certainly, if your child is attending class regularly, then she hasn't plateaued...If they are telling you the only way she is going to progress is to start training an insane amount of hours as a six year old, then THEY ARE FULL OF CRAP.
That is, unless the child is 6, competing L4 and training L10...To me, sounds like her gym should revisit their training curriculum.
I would never in a million years let my dd train 36 hours a week. Currently, dd is signed up for 9 hours a week. We are lucky if we make it to all 9 hours, so she's usually only there maybe 7hrs/wk. She is not 6 years old yet...but she is training level 5. We are at a very small gym that competes and scores pretty well...I'm telling you, if the gym that we are at can train a 5 year old to the caliber gymnast that my dd is at this time, then it is ABSOLUTELY NOT NECESSARY FOR ANY 6 YEAR OLD TO TRAIN 30 HOURS A WEEK. RIDICULOUS.