Have 340SEs + tp24 stands, 50lb sand each, 3 yo and 1 mo. No problems at all. Initially, I considered wall-mounted 170s for L/R for kids/safety too, but am glad I went w/ the 340s.

A metal brace for the back of the 340 seems like a good idea + maybe some earthquake putty. Otherwise, personally I'd go w/ wall-mounted 200s over in-wall/ceilings. But I can't picture your room/setup and have never really heard inwall/ceilings used as mains, so I hope it works for you.