ok so the size0 carseats birth to 9kg? what happens when ur baby gets to 9kg and arnt 9 months..?? do u keep them in the rearfacing seat or go to forward facing.. because the rear facing says up to 9kg.. is it dangerous to leave them in rearfacing fast 9kg? should you move up to 9months to 4yrs even if your baby isnt 9 months?? what is safer??