Think size 4 a baby needs to be minimum 20lbs . There’s no way a 5 month old is 20 pounds lol . My baby is 3 weeks younger than Harper and just in size 2 this week and 11 pounds . Harper looks similar size to mine so say they way too big lolMy 4 year old was in 7 pull ups before training over a year ago.
I think they were in similar nappy size to baby Reid in a similar timeframe.