​White hollow plastic object with sliding part, approximately 6cm wide found in my 9mo’s bedroom

No idea what this is, Google Lens appears to be struggling as it’s a pretty generic shape and colour.

Found in a 9mo’s nursery, any ideas what this is or what it comes from?

The room used to be my office and there’s a cupboard in there with officey stuff, so it could be from that too.

Final picture shows a poker chip on the object for scale.