I think Katierose means "bike". Her use of "they" refers to the children, in that her sim children disappear whenever they ride their bike.
Also, Katierose, can you please try to use proper capitalization in your posts please? It makes it easier to read, in general, and you may find you get better/more response. Typos happen from time to time (I'm good at those) and we certainly don't expect perfect grammar from everyone, but there's no reason to not use capitals at least at the beginning of your sentences and for the first person singular "I".
