Today the Free Realms web site is having some connectivity issues, resulting in players not being able to login to the game. Pex has been posting updates on the situation over on the official forums. If you are already logged into the game, you will be unaffected as long as you stay on.
Stay tuned for further updates!
UPDATE 2:30PM PDT: Well, it currently appears like the web site is up, though a tad sluggish. If it becomes unstable again I'll post another update. For now, get in the game and enjoy!