I don't exactly know myself, but I assumed they would go up till toilet training, which in my mind, is around 15-16kgs???? DS has been sitting on around 11.5kg for about 4 months now, so your DS might sit on 12.5 for months and months

I've been buying cloth as well lately (as I am pretty new to cloth too) and I'm buying large ones for DS, because even though he may only be in them for like 6 months or something, I can use them for the next one...

Sorry I can't help very much - website isn't very forthcoming with that information is it!!