On the Garden route you have Jeffries Bay at one end and Gordon's bay at the other which both have good vibes - Jeffries Bay is the big surf beach in SA but is fairly undeveloped - aimed at the singles crowd more than anything (big plus is that stores like 'quicksilver' have discount outlets here), but very chilled. Gordon's bay far more developed - check it out on the web. If you wanted to 'do' the garden route from one place to the other, then plan to stop off in Knysna and Plett on the way (Knysna very relaxed, Plett supposedly sophisticated but not exactly French Riviera IYKWIM). At Plett there is a great restaurant on the beach (surprisingly the only 'proper' beach restaurant we ever found in the whole country).
Rocktail Bay is the current hottest spot in SA if you want to be pampered and I think it is ranked as one of top 10 beaches in the world but it isn't a kids 'bucket & spade' job - it is serious luxury lodge with dolphin spotting and diving and stuff thrown in.
My personal favourite is Zimbali lodge, mainly because it is private and you can ride the hotels' horses without restriction across the beach when it is quiet. Seriously fabulous hotel with unbelievable infinity pool.
Try somewhere like zuluconnections.com for details on places like these if you want luxury. not sure how kid-friendly either are as we came back to UK when we decided to have kids.
Avoid East London, Durban and other built-up areas like the plague - nasty nasty nasty. You will not feel relaxed on the beaches. FWIT I also hate Cape Town itself - don't care what the guidebooks say, for me it is a Hellhole where they try to shove all the tourists onto the Waterfront which is just a nasty bunch of tacky restaurants of the like you find in shopping centres & mutli-cinemas. Great if you want a KFC. yuk yuk yuk. Long street in Cape Town ok but has an edgy vibe to it that anyone other than a backpacker might get a little concerned about.
November still only 'warming up' on the Garden route and you might spot the whale migration if you're there at the beginning of the month. Locals don't go on vacation until 10th December so you will have no problem finding accomodation as you go along (unless you decide on one of the luxury places which do get busy at weekends) - I wouldn't bother with self catering unless you definately want to go to just one place and stay there.
Water won't be as warm on Garden route (in fact could still be quite cold) as it will on the East coast around Zimbali lodge way (round there weather is kind of tropical all year round).
There is also a small town just 5 mins drive north of Zimbali lodge (but the name escapes me) which is a quietish holiday place - not as large as Gordon's bay but quite relaxed and surfy. Will be dead in November during the week, ok at weekends.
Yell if you need any more info
Also think about Sun City trip - totally over the top but very funny place to visit - great pools to chill out in if you stay in palace of lost city, and good alternative to doing the full-on safari thing (which I'd definately NOT recommend with kids at ages yours are at).