I ordered 6-12 months for my 5 month old and they are huge, but she can absolutely grow into them.
I bought the 3-6 months watercolor for my daughter, it was super cute but very large. So I bought a 0-3 months because I love the print and won't mind her wearing this and the larger size when she grows into it. The 0-3 still has room for her to wear it a couple more months and she is 5 months old now.
They are so soft & great for babies that sweat! I'm officially LS obsessed. & ordered 2 more times!
We love these!