Now that my son E- is officially 1 year old, hopefully he's sturdy enough to not require conversations like the following to take place between his 7-year-old brother D- and his 4-year-old sister M-, with D- giving his best approximation of my explanation of the fontanel:
D-: No! Don't touch his head! Remember there's a part on top where he has no head bone, and if you touch it, you're touching his BRAIN, and then he'll be crazy forever?!
D-: Yeah, you know, like....
M-: Like he says, "Uhhh, spaghetti is macaroni, ummmmm..."?
D-: Yeah, just crazy; like his brain doesn't work right. So just don't touch his head.
You may enjoy my previous M- conversations, D- conversations, and (wife) J- conversations.