Check...and Mate, I believe...

Me:Right son, this is a chess board and these are called chess pieces. These are yir pawns yeah, yir soldiers like, and these fellas at the back are yir heavy armoury. You've got yir Rook here, or Castle if you like, the Bishop here and, yeah nice Horsey, in fact it's called a Knight...next is the Queen and King..

5 minutes later...
Me: And that's basically it son, get the king into Check Mate!...now, the easiest thing would be to just start playing and I'll go over anything that's unclear as we go along..

Right, I'm White so I go first..This is called the "Queens Pawn Opening", right, now you...
No, the pawns can only move forward, one square at a time, not sideways, not backwards...no they can TAKE diagonally forward but can only move forwards..ok, that's called the "Anti-Borg Opening" ( I kid you not )...
Right, my go...Now, see what I've done? I've moved this Pawn forward to allow my Bishop and Queen to come out?...
right, you know you CAN move another piece you know?...OK, OK no..that pawn can only move forwards, it can Take diagonally forward...
OK, my go...now, see I've moved my Queen out and am threatening your King side?...your go...
No, it can't move backwards, only forwards, look, try moving another piece will ya?...OK, but you move that again and I'll have it...
Now son, see how I've moved my Bishop out now and have triangulated my attack on your King side?...be careful I'm about to...
OK look, you've moved that pawn again and I've warned you and I'm having it out!..

2 minutes later..
there's chess pieces scattered over the floor, a 4 year old sobbing in his room and me in the garden trying to get my breathing under control, throat hoarse..
Missus: Well, what did you expect?..What the hell were you doing anyway?...He's a 4 year old for Christs sake!
Me: Well, you read about it don't you...
Missus: Go upstairs and apologies to your son...play trains with him or summat..
Me: ...becoming Masters at 4, Grand Masters by 7, paying off their parents mortgage by 8 and retiring by 10..
I slope upstairs...
Later
Me: So love, do you fancy playing with me?
I reach for my Bishop.