RE: Help with sizing for a toddler!
DS is 28 lbs and 36.5 inches so he's also tall and skinny. For tops, he wears 2T in Gymboree and 3T in Gap/Old Navy/Land's End. He's in 18-24 month pants for most brands and they are just the right length. I picked up a shirt for DS at the Gap Outlet last month in 3T and it was definitely bigger than the 3T stuff that I've gotten at the regular BabyGap stores, so I think sometimes the outlet sizing can be off. I think you can get away with shirts being a bit big, but I would probably size down on the pants. The problem is not so much the length because you can always roll them up but if the waist is too big, then they'll fall right off. HTH.
Mommy to 2 DS's (2003 and 2007)