My daughter is 38.5 inches tall and weighs 32 pounds, we are a size 3t and they fitted well at first but then the waist stretched a bit. Maybe 2t would fit better. She hasn't worn a 2t in over a year. The black doesn't show through, but they're not as thick as the Target leggings. They have a great true Capri length. I don't think you should go up a size, I would stick with your kids normal size or even a smaller size if you usually order a size up. I don't feel like they're going to be huge, just a little big. Update: It's been 5 months and my daughter is now 3 years old (size 4t) and the 3t leggings fit perfectly! These are good leggings, I would recommend them! They have been washed and worn decently. They shrink a little with washing, but not much! I've upped my rating to 4 stars because they're holding up pretty well. They're a little thin, but that wasn't a problem.
Adorable and comfortable Splendid girls' leggings for kids and babies
80 Review
Lilax Girls Basic Length Leggings Girls' Clothing in Leggings
52 Review
IRELIA Girls Leggings Modal Spring Girls' Clothing for Leggings
52 Review
Girls' Clothing and Leggings - Govc Winter Fleece Velvet Leggings
49 Review
Amazon Essentials Little Short Sleeve Leotard Girls' Clothing for Active
61 Review
Thermajane Girl's Cozy and Comfy Thermal Underwear Long Johns Set with Fleece Lining
46 Review
Hollhoff Gymnastics Playgrounds Shorts - Breathable Clothing for Girls
48 Review
C9 Champion Girls Supersoft Bright Girls' Clothing and Active
46 Review