Mom and Dad!!!!

How come when you are younger your parents don't want nothing to do with you? I have asked this question many times and I still don't have an answer. Now that i am grown up an almost 21 my mom and dad are trying to be a part of my life. It's something Im not use to an I don't know how to take it. My dad calls me alot in one day to check on me and my mom calls me on her days off of work or before she goes to work to check on me they have never cared before an now all of a suden they care. My dad has been coming to visit me when he can and my mom has been at my house like every weekend for awhile now. Its kinda scaring me that they both want so much to do with me now but didn't want anything to do with me when I was younger. My mom is going to come an spend my birthday with me an she never really celebrated my birthday when I was younger. An my dad is also wanting to come an take me somewhere for my birthday. I don't know what they are up to but it is really really scary. I am trying to give them both a second chance but after all they have put me through when I was younger its kinda hard to give them another chance.