The brakes not working, does this mean I need new brake cables?
Well, usually, it does. Mostly, new cables will do the trick (installing them, however, is not always easy - this very much depends on the stroller you own).
I would, however, start by cleaning and lubricating your stroller and of course, the brake. If it still doesn't work, I would actually ask the store you bought it into, or make a video of the problem and send it to the stroller brand's customer service (in an email, you can also upload the video on YouTube and send them a link). They should help you by stating what can be wrong.
And, as I already said, it will probably be the cable, if cleaning the brake didn't help... but it also can be some kind of broken plastic etc., so best is to consult with the store and their potential repair service or technician.