What to tell to a kid of 6 years about Giuoco Piano opening? Isn't it to calculative or aggressive for a beginner of 6 years?
My daughter is a 1400 now, and we have studied openings very little. She knows a few names, but little else.
I teach opening principles. In ten moves, you should have advanced both center pawns, developed all four minor pieces, and castles.
Just that is enough to get her a decent position out of the opening in most games.
I'd explain nothing about openings to a 6 year old, except maybe something about using all your pieces (but it'll fall to deaf ears, most likely).
I assisted at a local school tournament recently, where players of about seven had a lot of trouble playing legal moves, or checkmating their opponent when being up almost everything. Checkmate is often not recognized and whole phases of the game had both kings in check...
The key point is that they must have fun, and they usually want to go on hunting expeditions with their queen. That is fine. It's a game, and they're six. My seven year old does not want to play games where she can't create new rules on the fly, period.
Once they ask, you can show something like the Italian and explain that it gets some pieces out. That is enough.
But please, show them lots of other things as well, up to move 3 or so (when they ask). I hate to see those kids matches that always start 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.d3 d6 5.Nc3 Nf6 etc because for both of them that's all they know. That makes the game boring, and the main thing should be to have fun.
I don't think concepts like "too aggressive" or "requires too much calculation" really apply to openings for six year olds...