Thicker tights are ideal for spring and autumn. My daughter currently fits a size 5T and I bought a size 7-10 thinking that something more would fit and she would grow up in. She fits a size 7 with some shedding and her other tights fit perfectly at this size. Well they arrived today and were quite large but I am not returning them as they are excellent quality and value. Right now I'm ordering a size 4-6 and still I think she will have plenty of room to grow before going up a size. So yes, there is no need to increase the size in that order! Excellent material! Cute design too!