I originally bought the 4mm bracelet for my 9 month old, who is very small for her age.  I was disappointed when I tried to put it on and it was just barely too small.  That being said, the construction of the bracelet was very sturdy and beautiful.  I have regifted the bracelet to a new baby in the family and it fit wonderfully.  I have since purchased the 5mm bracelet and I am looking forward to having it on my babies arm.

Update:

My 3 year old still wears the bracelet to this day.  The clasp still functions properly after 2 years of use.  The bracelets shaping has gotten a little worn out, but on her wrist you can't see that.  One of the pearls broke off somewhere along the way, but again, it is not very noticeable.  I would purchase this again in a heart beat.