Kind of an FYI / update. Took my M to see the grandchild this weekend. The IQ was what I expected and I used, at various times, the 22, the 40+adapter and the zoom. Did pretty well with existing light. The "lag" between shots did make photos of an active young child challenging but, in balance, the lightened load of not bringing my big kit was still worth the tradeoff. Maybe next trip I'll bring the big guns......
That bit of "lag" is the primary reason why the M is really only appropriate for situations where you are, essentially, doing one shot type work. It does work fine with bracketing exposures, but when you are shooting and looking for any kind of feedback between shots it is limited.
I've tried the Image Review "Hold" workaround suggested by another poster, but I didn't particularly like it myself and didn't feel that it solved the problem suggested here. I've tried turning image review off, but that doesn't eliminate the black screen lag between shots when the shutter fires.
My experience with the EOS-M and our active toddler has generally not been positive. I have some great shots with it when I can catch him sitting relatively still at play or on somebody's lap. But, trying to get an in-focus shot when he is playing actively is a real challenge. Lag between shots can be frustrating as well, as great expressions or interaction with other kids always seem to occur while I'm waiting or the camera to process the previous shot and be ready to fire again.
My 6D in AI Servo mode with the 24-70mm 2.8 or 50 1.4 are my tools of choice for active kid shots. While the 6D isn't noted for its AF prowess, I've found it does a really good job with kids.
I still love my M for other purposes. Its a terrific portable camera with high IQ to take with you for general purpose photography - pretty much for anything not moving quickly or randomly.