Looks-wise, goldies have long, wavy hair, whereas labs have short, smooth coats. They are similar size and both shed hair, but labs shed more (or it seems more anyway - those hairs get everywhere, especially the black ones!) Labs often also have more of that traditional "doggy" smell than goldies, as they have naturally oily coats as they were bred to retrieve game from water. Both are lovely breeds and very people-oriented, and are good with children, but labs tend to be a bit more manic and boisterous. Goldies on the whole are a bit calmer, and would be my first choice with a younger child. With both breeds, it is vital that you train them from day one not to jump up at people (very tempting to let the cute pup do this), as their naturally exuberant natures will make them naturally want to do this and when they're fully grown they will be capable of accidentially knocking someone over! They need lots of training to walk nicely on the lead as well as they are strong dogs when adult and will turn into pullers otherwise. Good puppy classes will help with this - you must take your pup to training if you get one.
The main health problem both breeds can suffer from is hip dysplasia - you must, must must get a pup from parents that have been screened for this. Basically, the parent dogs will have been x-rayed and their hips given a "score" - either a score for each hip (eg 8 and 7) or a total (15 in this case). The best score is 0 but this is very rare. The worst for a goldie would be 53 for each hip (so combined score of 106). What you're looking for is for each of the parent dogs to be below the breed average, which is a combined score of 20. If both parent dogs' hips total below 20, there's a reasonably safe bet that their pups' hips shouldn't become problematic. Ask to see certificates to show proof of hip scores, and if they haven't got them, walk away immediately. Google hip dysplasia in dogs and you'll see why you don't want a dog with it.
Goldies can also suffer from an eye disorder called progressive retinal atrophy, and again parent dogs should have been screened for this - any dog with it mustn't be bred from. Don't be daunted by this - all pedigrees come with their risk of genetic disease, and as long as you go to a reputable breeder you will have done all you can to minimise the risk of your pup being affected. This is why it's so important never to buy a pup from an advert in the paper from someone who's just a backyard breeder because their dog's cute and their mate fancied letting his dog be a stud dog, and neither thought to get any of the tests done. If the thought of these issues puts you off completely, you're back looking at the good old mongrels in the dogs' home, who will have lots of quirks but should be free of genetic disease...