Just in case you were wondering, Hot Wheels color shifters CAN go down the toilet with no apparent plumbing problems. Just in case you were wondering and all.
This was the culprit. The purple / white Dodger flame car. To make this car change colors, you have to put it in cold water. Well after Zach had sufficiently soaked the kitchen table and the kitchen floor (along with everything else nearby) - I shooed him away and told him to put it away for awhile.
Except he comes back later, visibly upset, that his car has been flushed down the toilet. This is what happened (according to him). He was in the bathroom with Addison while she was going potty. He thought he'd be nice and flush the toilet for her, when all of a sudden, the car slipped out of his hand and into the potty. According to him he WASN'T trying to put the car in the cold toilet bowl water to change it's color. Mmmhmm. LOL!
Knock on wood, it seems to have gone down the pipes with no problem. Not sure how, but it did. Guess we'll see if it eventually becomes a problem! KIDS!