They can go in when they can hold their head up very well (usually 3 months +). Kathryn wont stay in for all that long, but it's very useful for when I'm fixing lunch in the kitchen, or for when we go to restaurants (still can't sit in a high chair) and we have the tray with it so she can play with toys (and it helps to keep her from tipping it over). There are other brands that are less expensive, having a seat that they can sit in before being able to sit up is very useful. Like when kathryn was 3.5 months she really hated when she couldn't see me, so I'd stick the bumbo in the bathroom so I could pee without her freaking out.