its diff. for each baby, but generally around 4-6 months. Remember that baby's spine is very soft. When it hardens, the back and skeleton is able to support the body. Always keep baby on the floor on their tummy as much as possible so that the spine is kept straight and long. This keeps the spine from curving. Many parents love to use baby furniture that keeps baby's sitting on their tail bone. This is when the spine is beginning to firm up.
Often, chiropractors will find that childrens spines are curved, but this can be avoided by keeping little ones on the tummies instead of upright in a seat. Keeping them on their stomach in a prone position also allows baby to exercise their neck, arms and legs. This is useful so that they are able to use their energy as well. :)
at 11:44 PM on Jun. 5, 2009