I want to purchase 3 or 4 either a 7-inch or 10-inch Android tablets for my grandkids ages 6, 6.5, 7.5 and 10 years of age. I'm looking for something that will work well with educational apps. I would like to spend under $200 each. I need recommendations on CPU and Android OS version, as well as trusted sellers if you have them. The ZT-180 was looking good, but now I'm seeing some bad reviews. Help!!