I just learned about these pajamas a few weeks ago and totally love them.  I bought 3 pairs for each of my 5 and 3 year old sons.  These pajamas run small like most tight fitting pajamas.  I bought the size 5T for my 3 year old who wears 4T and 24 months for my other son who is 1 and wears 18 month size clothing.  We might have gone up to a 2T, but my son wears 12 month bottoms so I stayed with the 24 months so the bottoms would fit.  The bottoms fit with room to grow, the top fits perfectly.  We normally wear Carter's pajamas and I have to say that I like Leveret Pajamas a little better because they are soft and the bottoms don't fall off my baby.
We just got the size 2T PJs for Christmas and my son fits them fine and the 24 month size perfectly.  I should have gone with 2T when I originally bought these.  The waistline is a bit bigger in the 2T than 24 month, but the pjs fit snug so not too worried about them falling off.  I also like that the 2T top gives more room in the length for torso.  Don't have to worry about the arms being too long as they also fit snug and bunch up.  My son still wears 18 month clothes and can wear some 24 month tops now.  The 2T size could have been big in Oct when I first bought, but fits great now.  In hind sight, going larger would have been fine and he could wear them longer.