At 4 months, a baby typically can hold his/her head steady without support, and at 6 months, he/she begins to sit with a little help. At 9 months he/she sits well without support, and gets in and out of a sitting position but may require help. At 12 months, he/she gets into the sitting position without help.

Every baby learns at a different time, the worst thing you can do is compare your baby to another.