Simple bike hack…literally.  Thomson seatpost boxes make very good hacksaw sleeves, making them safer for travel and keeping the kiddie’s fingers away from the blades.
A little packing tape around it a few times adds some structural integrity and closes off the end.  Another pic after the break shows there’s room to grow, making this a versatile opportunity to use cardboard in an environmentally responsible way. Reduce, reuse, recycle…that’s our motto.
While I keep mine buried past the handle (per the first pic), the box is long enough for a regular saw if you don’t cut it down like I did.