This was stuck on the underside of the lid of a laundry basket I picked up at a garage sale. I'm sure there are bigger issues to deal with than just the risk of suffocation. What about sorting out those over-protective motherly cravings that drive you to shut your kid in a box in the first place. Why don't you build a nest, put him in it and sit on him with your post-natal fatass while you're at it?
Oh, and about the sticker placement...what, you want them to actually place the baby inside the box, and when they're on the verge of putting the lid on, they see it and go, "damn". Honestly, if your demographic includes baby-boxing-boneheads, then put the sticker on the outside. Hell, get a midget (not a baby, that would just be wrong) to pop out of the box after shipping and stick it to their damn faces.