How old is your LO/how much do they weigh/and what size are they in?
My 3.5 year old is in mostly 4T but can wear some 3T and even a few 5T items, depending on the brand. I have to constantly go through things to make sure I'm not missing something in a bin that could fit, because sizes are so crazy.
LO2 is almost 2 and she is in 2-3T, 3T in leggings because they are tighter, and I think they fit smaller overall. She has some 24 month summer items from last year that I held up to her the other day, and they still seem like they would fit...however, warm weather is several months away so I bet I'm out of luck thinking I can squeeze her in them this year. I made the mistake of getting rid of some things I didn't think would fit her this winter, from her sister...so I'm definitely waiting until the last minute to sell anything.
I'm thinking LO1 will stay in 4T for quite some time, and LO2 will be in between 2-3T over the next year, depending on how she grows and what the item is.
LO1 is 30lbs give or take, and LO2 is 22-23 pounds maybe.