My younger nieces love both of the Raving Rabbids games. Elebits is also a great game that's meant for kids, but I like it a lot too. You have to run around looking for little creatures to collect with your zappy gun, and you have to throw stuff around and make a mess to find them all because they hide. It's super cheap now, too cause it came out a while ago.:biggrin2:
Link's Crossbow Training is also a lot of fun. If you don't want the cheesy plastic gun thingy, you can get just the game used for only $3-5 at GameStop.
Also, do you have you Wii connected to the internet? There are a ton of games available for $5-15 for download. There's a huge collection on the Virtual Console which is older games from NES, SNES, N64, Sega, and a few other old systems. And WiiWare has new downloadable games. Like... Mega Man 9 styled after 1 and 2. Utterly fabulous!
I usually wait for prices to come down, but I will probably get De Blob and Wario Land Shake. They both look great and would be fun for kids too.
Oh, my sister loves playing We Ski with her Wii Fit board. That's another good kid/family one.
I also don't care for Wii Play, I think we played all the games on it once and put it away.
I love my Wii and play it all the time. Currently addicted to Trauma Center: New Blood. Mmm, emergency surgery with a Wii remote... Bit hard for kids but it is clean/safe and anime-styled, not realistic, if you're curious. The first one was great and is pretty cheap now. I also love anything involving shooting zombies but you might not consider that child-appropriate.