1) same style, but different colors - mostly t-shirt
2) exactly the same style and colours but of course different size - t-shirt, jacket
3) or sometimes, different style, but wear same color theme clothes together
for 1) and 2), usually from kids clothing department, but the sizes are S, M, and XXL (more comfortable than XL for me as sleeves are longer)
yes, especially the younger the age, the more that they like to wear the same clothes with dad or mom. my younger daughter will take out the clothes the night before and suggests to wear the same clothes the next day. she was quite disappointed when she found out her "same" clothes not fit her anymore last Friday.