You;ve stated the who you photograph, now time to state with what:
1. External lighting? Most mirrorless except Sony Nex high end does not really work with speedlights
2. Where - mirrorless are great outdoors
3. Focal lengths and aperture. It cost a bit more for fast lenses in mirrorless...if you have invested in Canon glass its even more tough to switch away.
4. Except the mid to high end bodies with good lenses and phase detection, don't expect continuous focus to work. No problem if your kid is old enough to pose but mine don't.

I have Nex 3 with kit lens and 60D with a few lenses and speedlights.
I use the Nex 3 only during holiday trips when I don't drive, which is like once in a year...lol