Ahh, an area that I have some level of expertise in. Depending on how much gear you have and how many lenses you want to carry (which I assume if you have a kid running around, you won't carry a lot of lenses). I have a 2 yr old and now a 2 month old and the most important thing for me, is ease of access. For that reason I use a Mindshift Gear Panorama Rotation 180 for mine. Keep the camera and few lenses in the beltpack and the top of the back holds diapers, bottles, snacks, etc for the little one. Very easy to access gear with the belt pack, don't need to take the backpack off. I had an f-stop bag for a while and they're great bags but not easy to access.
With the Mindshift bag when I had my D810 I had it plus a 24-120 mounted and a prime (50 or 85). Take the camera out, take a few pictures, then put the camera back in. Have a nice separation between gear and kids stuff at the top. If I go out with the wife she'll be able to access the gear without me taking the pack off, otherwise it's an easy access for me. I'm also looking to pick up the f-stop Kenti again but that looks like it'll hold less kids stuff but more lenses.

