I'm not gonna tell you what to do w/ your kid, but a couple notes worth mentioning:
-The Magpull stock LOP is around 13". This is A LOT for a 6yo. My kids (7 & 3) both have Rascals and even 11.25" seems like a bit much. Especially, in the colder months with jackets and such.
-My kids have plenty of other firearms to use, but I try to keep them to iron sights, for now. A random plinking w/ a red dot does happen. I feel it's paramount to start at the basics and get skills and fundamentals nailed down. It's too easy for them to get distracted from these key things when they have a semi-auto w/ a magazine full of fun.
-By the time you're all said and done (stock, threading, trigger, mount, dot/scope) you could have started w/ a very good bolt trainer for much less. Just saying