DS (about to make me a granny) grew his hair in secondary school and had totally natural, totally gorgeous glossy chestnut ringlets below shoulder length by GCSE time. Nobody ever suggested he might be happier as a girl. He got a key role as a royalist cavalier in the summer historical pageant set in the Civil War.
He decided to grow it; he decided when to cut it - at about 17 and doing A levels iirc. I think he wore a hairnet for science and food tech lessons. When it went there was a huge saving in shampoo and conditioner!
Please let children do their own think and find their own labels if they want them. I worry about the channelling going on, especially for younger, more impressionable children.
Hair is just hair.