Just wanted to say In my experience lil joey and rumparooz do not fit at 4lbs. My daughters legs were way too skinny, she was 4lbs 3oz and didn't hit 6 until she was 2 months but I did actually like the lil joey cover(is the cover lil joey or rumparooz? Lol) much better than any other nb diaper or cover I had because you can do the one size newborn hack with it to make it smaller to fit a preemie better. It's funny because now her thighs are the only chunky part of her body, she's 15lbs now at 7 months and we use the esembly size 1 now and its hard to fit the inners around her thighs as is but when I roll the elastic inwards the space for the legs widens up and they fit her well like that because she has such a tiny waist and sizing up would be massive on her narrow lil belly shes only on the second snap from the center. But this is actually helpful if the one we are currently pregnant with ends up being bigger so when they estimate size closer to when we are due we can get an idea of what may work the best so thanks for the info for the average size and bigger babies!