These are all very good suggestions. On desktops you can already change your background and colors settings for the homepage, but we don't yet have it for mobile devices which is something that needs to be done.
The best way to protect your KidzTalk username is to register for an account. Registered users may have an avatar and points next to their name to verify their account. We can look at preventing other people from using a username that is already registered, but it is difficult to identify a "scammer" user, since people use different devices with the same username. Since all posts are moderated, we do block any that don't seem right, but they can be missed if we think it is a valid post, so be sure to flag them if you see something suspicious. However, you need a registered account to flag posts.
You don't need an account to view user profiles. For example, we have a directory of active KidzNet users and clubs. However, making it easier to access sounds like a good idea.