Well it comes from a poem by annie mg schmidt(famous children's book writer). https://www.margriet.nl/in-en-om-het-huis/koken/doosje-annie-m-g/ It kind of means when you find someone very cute/nice etc you want to stop it in a box so it always with you. It sounds creepy but it isn't
Certainly not as creepy as "I could just eat you up!" In English expressing a similar feeling.