We have both the PS4 and Wii U and my suggestion is, if you're gonna factor kids into the equation, get a Wii U.
Too many glorious games on Wii U that you'll cherish with the kiddos. Someone mentioned Diablo III for PS4 - um yea, not really appropriate for kids that age. Knack is great and kids would love it. Of course there are the LEGO games. But really, you need a Wii U.
Mario 3D World
Mario Kart 8
Rayman Legends
Donkey Kong Country
Captain Toad
Splatoon
etc, etc
Let your kids be kids a while longer. They'll be playing GTA 6 and Black Ops 32 on your PS5 soon enough!