So my two year old is in the 5th percentile, meaning she's tiny (think about 25 lbs) and my two month old is in the 95th percentile (at 13 lbs). DD1 didn't weight that much until she was four months old! DD2 is already in size two diapers and only 3 pounds away from size 3, which DD1 still wears! Both my girls are going to be wearing the same size diapers soon, even though they are two years, two months apart! Because I definitely see DD2 gaining 3 lbs and moving up before DD1 does the same. Anybody else have this?
Re: DD's big little sister
Well, sort of.
My DD was in size 4 diapers from 4mos-26mos (we PTd last month) as she was also a big baby but then just thinned out as she grew taller. I had like 10 diapers leftover but I figured I'd save them for DS when he needed them "one day".
Yeah, he'll be 3mos old on the 17th and he moved on to the 4's today! So I almost had them both in the same size diapes at the same time
Darn PTing 
well DS was always very tall and thin. 90th for height and 30-50th for weight. At DD's 2 mo appt she was 13 lbs 1 oz, born at 7 lbs 1 oz. She gained 6 lbs in 2 months! She is 90th for weight and 50th for height. People laugh when they see her rolls, since everyone always asked me where DS's rolls were...he was so adult looking at a few months old--no baby fat.
DD is in size 2 and almost in 3's. DS is in 5's.