I just showed my 7 year old nephew all the reveal trailers. Here is his reactions.
Villager: my nephew was confused. Didn't see how he could be a fighter.
Sonic: my nephew got really hyper. He loves sonic.
Little Mac: "He looks so boring. He's just a puncher". I tried telling him lots of people are excited for Mac, but my nephew didn't care.
Mega man: didn't know who he was, confused him for kid Icarus(?)
Greninja. He was loves charizard, thought greninja looked cool despite not knowing who he was.
Pacman: thought he looked awesome. I was surprised he knew who pacman was. Apparently there is a pacman cartoon on currently?
Rosalina: my nephew was so happy. He loved her in SMG.
Robin and Lucina: didn't care about either, was obsessed with falcon
Shulk: He got excited. My nephew watched me play all of xenoblade. He wanted reyn in.