Admittedly, it is comical on face value. But the really funny part is that someone needed to put a warning sign on a sweater box. We could only surmise from this that someone had, in fact, tried to place their child into the box and, fearing the legal ramifications, the company was compelled to print a warning sign.
Just in case you couldn't figure it out on your own, your baby is not a Cirque du Soleil performer. He/she is not flexible enough to fit in that box. They may stand a chance, however, at prop comedy.