Hey hey!
Welcome brother!
You two will love bodyboarding I promise! It will also be a great way to bond with your son! Craig is spot on with everything there, I would just like to add the following, board size, make sure you get the right size. Nothing worse that having to ride an over sized "tanker"
A quick way to gauge size is to hold the board in front of you, ideally it should come up to your bellybutton (as Craig mentioned). See below.
Board size:
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Note that bodyboard sizes are measured in inches, so look out for that. I'm 1,74 and ride an 41" board, but later on you will find the size that works for you. I bought my 11 year old nephew a Science Pipe and bought it an inch to big, so that the board will last a bit longer. You know how quickly kids grow!
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Also...
Wetsuits:
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I prefer my wetsuits a bit snug, that way I know it's keeping the water out. I would say REEF offers the best value and quality, you can't go wrong there!
Fins:
Make sure they fit snuggly but not too tight, also not to loose. Get fin savers, then you wont lose your fins in the water. You
WILL get blisters, but it gets better after a while, I am yet to own a pair of fins that doesn't give me blisters. The easy way around that is to get fin socks, the REEF ones work really well. You will have to try the fins on, what works for you won't necessarily work for me.
REMEMBER: Respect the ocean, never get yourself into situations you can't handle, if the swell looks to big, leave it, tomorrow is another day, this is Cape town after all and big swell isn't rare...."When in doubt, leave it out", never surf alone, speak to locals and learn from them, and always wear sunscreen!
Maybe also grab a bodyboarding DVD, it's a great way to get you amped for a session and you learn a lot.
Most importantly: HAVE FUN!!!
See you in the water bru!