In my opinion, I think it's because of the meaning of the name Dora, it means gift in Greek. Many people see children as gifts due to the joy they bring to couples. Check out http://en.wikipedia.org/wiki/Dora_%28name%29.
dora is small just like they are. she also has time to explain things to them in terms they understand. she does things they are interested in or would like to do. and she teaches them things in ways they understand. sounds like a good friend to me.
Because she has boots as her best friend .. My daughter goes nuts over Dora and boots and she's only 19 months old. Dora has the squeaky voice and gets excited over the little things that's why kids love her so much.