How would I get the players Id in-game by saying a command?

Can the command be :Id (player name)

I have this so far but I don't know why it won't work.I also don't know how to add a part so that if I say :Id (player name) it will give me there Id.Also I want it to only work for certain people.

while true do
wait(1)
g = game.NetworkServer:GetChildren()
for i = 1,#g do 
print(g[i].Name) -- g[i].Name is the ip... this is good for banning people by ip.
end 
end