ROT 13 encoding and computer basics for an 8 year old

I showed my daughter how to write secret messages using ROT13.

If you haven't heard of ROT 13, imagine cutting an empty toilet roll in half
(vertically, so you still get 2 cylinders).
You write: ABCDEFGHIJKLMNOPQRSTUVWXYZ on one.
Then: ABCDEFGHIJKLMNOPQRSTUVWXYZ on the other.
Line up A on the top one with A on the bottom one.
ROT is short for rotate.
Now rotate the bottom cylinder 13 letters ahead so that A is above and N is below.
Flat on paper this now looks like:
ABCDEFGHIJKLMNOPQRSTUVWXYZ.
NOPQRSTUVWXYZABCDEFGHIJKLM.
You can now us this to encode and decode messages.
HELLO would become:
URYYB
http://en.wikipedia.org/wiki/Rot13

I also showed her letters to numbers:
A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z.
1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26.

So here HELLO would become:
8 5 12 12 15.

Next I'll teach her that computers have character maps. ASCII.
A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z.
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90.

Hold down ALT and press 72 and you get H.
ALT 72 ALT 69 ALT 76 ALT 76 ALT 79 would become:
HELLO

Eventually I'll explain binary and how data is stored using electrical ons and offs.