I liked the IQ of the 5dMk2 a lot.
But the AF was awful not using the centre and/or moving subjects.
The 5dMk3 is an ideal allrounder, you would enjoy a lot taking picutres from erratic moving subjects like your kids.
1D MKIV, 1DX MkII, 5D Mk IV; lot of lenses, flashes etc
Fuji X100s, Sony RX100 III,
Fuji X- XT1, X- Pro2, XF 23 1,4, XF 18- 55 2,8-4, X- T1, XF 16/1,4, XF 55- 200, XF 56/1,2, XF 50-140, XF 100- 400