Isn't this what my parents are supposed to do not me?

I am a freshman in college i attend USF and i rent an apartment with my girlfriend. And i have two siblings a 13 year old brother and a 3 year old baby sister. And for the past two weeks my parents have been calling and begging me to come and tuck my baby sister in and it works she fall's right to sleep when i do it. I do not understand why she wants me so bad. This is what my parents are supposed to do not me. I only live around 20-30mins away from my parents so it is not that bad. I do not understand this why does my sister want me so bad? Advice?