We bought 4 of these for me and my husband and our 2 kids: 3 yr old boy and 9 month old girl. I was so confused on sizing because of mixed reviews and the sizing chart so I will try to help others out.
My husband is 5'10", 175 and usually wears a 34 waist and large shirts we got him an XL and they fit fine, maybe a TINY bit roomy. There is no lining and they fit more like trunks than board shorts.
My son is between 2T and 3T and we bought him the 3T and they fit great, like little euro swimmers, I LOVE them! My daughter is wearing size 9-12 months and we bought her the 12-18 months and it fits great, she has a little room to grow which is perfect since it's not quite summer yet.
I had the most confusion with the womens sizing. I am 5'5" 125 lbs 34 C, a little bigger in the hips, and usually wear size 4 in pants, usually an 8 in swimsuits (from stores like J crew) or a medium in swimsuit (from Victoria Secret) and based on the measurements on the size chart bought a large. Well it was WAY TOO BIG! I initiated a return and the seller was GREAT! They made it REALLY easy to get my correct size. I ended up with a medium and it is a little roomy in the chest area, I probably could have gone down to a small but I hate when swimsuits squeeze my hips so I'll keep it, the ruffle hides the chest anyway and it's tight enough that it won't fall down. It has a shelf bra with removable inserts.
The material is pretty thick but a teeny tiny bit see-through, not embarrassingly so but it is a white material which is usually double lined and this is not.
Are these REALLY excellent quality swimsuits? No, but for around 15 bucks, I'm very satisfied. For the price it is great quality and not much to pay for a matching set of swimsuits, I'm so excited to wear them together!