How to fix glass kaleidoscope inside cardboard tube
If the size of the mirrors is such, that it's already (sort-of) tight fitting in the tube, then you don't need much force to keep things in place. You may consider a kneadable adhesive like blu-tack.
An Internet search also leads to someone mentioning dimensional glue dots. Glue Dots are a name brand adhesive, sort of like stickers except the stickers are double-sided tape pieces, but also refers generically to similar products.

If all else fails, you can stick to the hot glue.