Both sites from a computer security standpoint are secure, but if you mean from predators etc for your children, then that's a whole different ball game. No matter what site they use its important to use common sense, and to teach users to not give out their personal information and not to meet people they have only talked to online.
Because MyPraize personally approves all usernames, photos, videos, groups, songs by hand their content is much cleaner. Also, they have administrators who scour the site for inappropriate content in the blogs, forums and Chatrooms.
There is never a "safe" place for children online in any social network environment. MyPraize's goal is to be the "safest." Allowing children online is a lot like letting them ride in a car. No matter how safe the car, how big, and how well protected, they are subject to risk. -Matt Gaiser (Owner / Partner MyPraize LLC.)