If your kid needs a really short lop, there really isn't a great option for an AR with a standard charging handle. A magpul CTR and The Larue RISR is pretty good if your scope height lines up with it. It adds about 1/2" to the cheek height. Your mount height may or not be tall enough or too tall. For all the positives it has, the extra springs make charging the rifle a bit more difficult. For a kid, that may or may not be a good trade.