A.C.
This sounds perfectly normal to me. My son did the same thing at the start of kindergarten and I was a little worried - but my mother, who is a life long elementary school teacher (has taught K-4 at various times), assured me it was very typical. Kids start to get a little freaked by the pressures of the "big" school and the knowledge they are growing up - it makes them insecure and they look for ways to be reassured that they are still your "baby." My son is in first grade now and still has his moments when he wants to be cuddled in my lap and talk in a baby voice, but he has mostly grown past the regressive behavior he exhibited earlier. As I recall, I tried to help him through that time by both allowing him those moments to cuddle and have "Mama time" - but also to balance that with talking up the reality of getting older/growing up and how many advantages come with that. I tried to continually portray growing up and being on your own in the adult world as a wonderul, adventurous, liberating thing to look forward to(e.g. told him stories about how great it was to move into my first apt. on my own and be able to eat dessert before dinner if I wanted to!). At one point he asked when we would kick him out of the house and I realized that was part of his fear - that he would be forced to move away from us someday! I didn't realize how hard it is for a five year old to think about living on their own. So then I had to backtrack and reassure him that we wouldn't be kicking him out - that he would get to an age when he would feel the confidence and desire to move out on his own and even then, he could choose to live nearby and we would still be a family and see each other as much as we wanted. That seemed to comfort him. So sometimes just talking it through - addressing some of those behaviors head on - can reveal fears that may be easy enough to address.
Good luck!