Every day my child repeats lining up toy cars in a row. I'm torn between just watching over it or inviting them to a different kind of play.

By repeating it, they may be confirming the arrangement or finding reassurance. First, imitate your child's way of doing it and enjoy it together. If it seems they'll accept it, suggest a small change — running just one car through a tunnel, or lining them up by color — and if they don't like it, it's fine to put it back. The aim isn't to stop the repetition, but to increase the kinds of play you can share while keeping your child's sense of security intact.