The size runs small.  I've purchased size 6-18 months for my 14 months old baby.  She's small.  She usually wear 6-12 months size or even 3-6 months (Gap Baby) size depending on brands.  They were small.  After one wash, they are even smaller.  This 6-18 months size is the same as Gap Baby's 0-6 months size.  I suggest you to buy 2 sizes larger than the size you need.  Fabric is not very soft.  But, they're thinner/lighter and 3/4 length that I was looking for for summer.