As previously mentioned, it's not a good idea to have the same password on many sites, since if the password for one site is compromised, all of the other sites with the same password become compromised too.
A nice idea is to use a single password that's easily remembered by you, and "salt" it with the name of the web site or application you're using it with.
"Salting" a password means inserting extra characters into the password to make it harder to guess.
So, you start with a password that you can remember. Say your son's name is Isiah. You may want to play with the capitalization, and maybe insert some numbers and symbols too.
Suppose I choose my password to be !s1aH (just replace the first i with a !, and the second i with a 1, then capitalized the H).
Now, say I need to create a google password. My salting method could be as simple as alternating characters between the name of the site and the password.
Result for google: g!oso1galHe. See... impossible to guess.
Result for yahoo: y!ash1oaoh.
Or, you could alternate three characters at a time:
google: goo!s1gleaH
yahoo: yah!s1ooaH
You can use any strategy you like. This way, you get impossible to guess passwords unique to each site/application, but only one password to remember.
Hope that helps!