Mattias did decorate his own cake, which we had later that night as a family. He decorated it to look like a NXT lego brick. (This means something if you are into robotics.) He had all the buttons, and the screen decorated onto it.
Here is one of the many robots Mattias has made. He attached a set of gears to it, built some blades at the end, and programmed it to spin. He used it to whip up some scrambled eggs for Sylvia.
Because I grew up in a family of 9, where every birthday, every year, we would play "drop the clothespin in the jar" for a party game, it now seems like you can't really have a birthday without some version of that game. So, here we are, since I do not stockpile clothespins like my pioneer mom, playing the game with some bean bags and plastic buckets.
Sylvia found a plastic cone in the beanbag game, and thought it looked like a "party hat". She wore it for the rest of the night. She couldn't move here head at all, so she kept shifting her eyes around like a criminal. :)