I bought these for my 4 year old daughter 1 year ago in size 6/6x (she is 50th percentile for height for age and weight for age) and they fit her perfectly. She is now 5 and they have held up very well over the year, still looking like new. I would have never thought to spend so much on underwear for a toddler but these seem well worth it as they last so long and she finds them so comfortable. We bought these in a local store last year and the 4/5 did fit her at the time but seemed that she might outgrow them and the 6/6x also fit well so we went with the 6/6x even though she was only 4 years old. The 6/6x from last year still fit her but she needs some new ones so I just bought size 7/8 online and will update the review to say how those fit her after they arrive. I labelled the fit as somewhat small as we went with one size up, however, even her size does fit her for her age just fine (but one size up also fit well and thus will last longer).
I am updating the review to indicate that the 7/8 we recieved a month ago fits my daughter well (she just turned 5) and when I ask her which she likes better (the new ones or the older ones in 6/6x) she says they are the same. I can see the 7/8 is a bit bigger but fits her very well too.

Our daughter LOVES these pajamas! The fit is perfect and comfy. Contacted Jackie at DoReMiFa - she was very helpful and pleasant. Definitely recommend these as well as esme girls panties.

Best Undies (if you wanna compare undies)

My 3 daughters have worn this brand of undies for about 14 years. Originally bought them because I read they were good for kids with sensory issues about their undies! They are extremely soft, no uncomfortable seams, and hold up forever! A bit pricy for sure, but worth the cost to me. I definitely think they run a bit small. My very skinny 10 year old is in the 10-12 now and they fit perfect (she normally wears an 8 or smaller).

My son says this is the best underwear and the only one he wants to wear. It is soft and has no seams and there is no tight elastic on the thighs. He made me get rid of all his GAP underwear. He is a normal built 11 year old and the largest size will likely still fit him for another year. I wish they would offer them for teenagers too!