I purchased the 18 months-24 months size for my 9 month old son who weighs 23 lbs.  He currently uses the 12 month size and it is a bit tight.  The 18 months - 24 months is perfect for him, and there is still some room for him to grow into.  The bamboo viscose material is so soft.  I highly recommend this item for your child.  It is worth the price.