Instead of just waiting around for the big milestones to occur, we want to give you something to do. Sit the baby up in front of you (supporting back shoulders, grab the overall suspenders, or whatever feels right) and dangle toys in front of him. Swinging at toys while seated is a brand new experience.
When he’s stable-ish, let him go (forming a protective ring around him so he can’t fall in any direction too hard)… now COUNT. 1, 2, 3, 4, 5… woohoo – 5 seconds of sitting. Now, rest.
If you are like me, then every day for the next few weeks you would write down how many seconds your baby can sit unassisted (until you get to about 120, then stop).