After having a thought how to fold just the head of Jack-Jack, I recalled diagrams for baby. This baby model is from Robert J. Lang's "Origami Design Secrets", folded from 125x125mm brown color baby. The final model is about 55mm height. Ops..I missed out a fold at his diapers =)
[Update] Due to popular request, I managed to get some spiky hair at the top, but the head is not 3-D anymore. As for the mask, I had to use additional paper for that =) And I fixed the "diapers". However, still missing his ears..