My keiki are obsessed with stickers. They love to put them everywhere (including the floors and walls). Thankfully we have that special paint on our walls that we can wipe off crayons/marker and stickers don't really stick that well and won't peel the paint.
This A5 sticker sheet is made from adhesive vinyl and is printed with eco-friendly ink & is waterproof. Depending on what your keiki puts them on, they can be removable but it is at your own risk.