I have an iPad, a Nook Color, a Sylvania 7" mini-tablet, and an Acer A100 7" tablet. If we'd had the stock I'd have an HP Touch Pad as well, but we sold out of them in 15 minutes as soon as the price was dropped to $149.
The iPad and Acer are the most useful with the Acer being more convenient and the iPad being more useful. Until converted to an Android tablet by rooting it the Nook Color's a dedicated ereader and B&N shows no sign of changing that. The Sylvania is basically a paper Weight with no capacitive touch screen and a poorly-designed screen interface (you can use stylus or nail, but results with my fingernail are often far superior to those achieved with the stylus). It is Android Gingerbread, but the Acer's Android Honeycomb has far superior response on a capacitive touch screen.
However, as an entry-level tablet, the Sylvania's going for $100 or less at such places as Big Lots, CSV Pharmacies, K-Mart, and a few other places (I got mine at Toys'R Us for $199). it does run Android, has an micro-SD port so is expandable (up to 32GB as I recall), and accepts 3rd Party apps so you have access to the Android Market. If you can pick one up for $50-80, it's a much better deal, especially for the kiddies (you should wait and spend your money on an Acer A100, A500, Motorola Xoom, Samsung Tab, an HP Touch Pad if you can find one, an iPad, or any of about a hundred other tablets that are going to be blitzing the market this Christmas season because, quite frankly, you're the parent and you get better toys than the kiddies do).