Bias will prevail.
Check the following. Do you have an HDTV. If not, then the Graphics improvement won't benefit you.
However, if you do have an HDTV then:
Wii is very family orientated. No bloody games, no mature content. Graphics are poorer than Xbox and PS3. However, they are well established on the games front wrt motion controlled games.
Incomparison on the Wii in terms of controller (motion), Kinect is controller free. you are the controller. However, it has some recognition problems. I am not sure of how big your kids are, but Kinect can experince problems detecting small people. It is also relatively expensive. coming in at R1999 for the connect and around R1999 for the base console. General games are well established, but kinect games are in the entry stage. PS3 is an expensive console, it comes in varying Hard drive configs. from 120 gig to 320 gig, and ranges from R2699 to 3899 (bundled). The games are well established, with few games on the Move at the moment. Graphics are arguably the same as Xbox, with both having exclusive titles to show off the hardware. Move starter pack comes in at R598 on Kalah.net, but you will have to buy an additional motion controller (out of stock for months now) at around R300. so if you have 2 kids, thats (R1498 - 1 starter pack + 3 controllers) The more action based exclusive for the Move, like Killzone 3 (youtube it) will require an additional navigator control at R350 per person. So in actual fact, it comes in very close to the cost of the Kinect. One feature you must be aware of, is the PS3 has a blu ray player. Both Xbox and PS3 consoles can be set up as media servers via PC or wireless.
So in short, if your'e budget is tight, then Wii, and if bucks is not too much of a problem, then Xbox or PS3.
Hope this helps.