"Vikings" never went to North America, but the Norse did. The term viking denotes the kind of pirates that you are thinking of when you say that they didn't go to fight - a viking would have gone there to raid and plunder and trade. This is not what happened in this case. This is how I recall the story (NOTE that it's been a while since I read up on this part of Sagas of Greenlanders): The original discovery came about because a Norseman on his way to Greenland was blown off course in a storm and saw that there was land to the west. The idea was, that if there's land (rather than the end of the world), there may be trees, and lumber was something the Greenlanders needed very badly. Therefore people went back to look for lumber and other useful things at a later date. Because of the weather, in places like Canada, going back means you have to stay a season, since the ice will trap you, so that's why L'Anse Aux Meadows was settled. The idea was to collect wood and such and if there was anyone to trade with, then also to trade with them. This is where the story goes awry, since the fleet was hit with a bad storm on the way over, and many lives were lost. When the indians met up with the Norse, the first thing the Norsemen did was - according to very old Norse custom - invite them for food and drink. The drink on hand in a ragular day was some form of dairy, to which the indians were intolerant. They got sick, and thought the Norse had tried to poison them. Since there were many more hostile indians (who didn't wish to trade after the poisoning incident) than there were Norsemen (due to the loss of life during the storm), and since the Norsemen found the place disappointing in terms of what they could use for Greenland, they left. On the way home the indians attacked them, which sealed the deal. Leif Eriksson said he did not want to return, but his sister Freydis went back with two tradesmen brothers, but due to the infighting between Freydis and her brothers, and the raids by the indians, that expidition left, too. They too lost many lives, some to a bad storm again (I think) but this time it was mostly because of the infighting - they killed oneanother off, simply put. After that, nobody went back again, partially because Leif said there was nothing there to bring back, so nothing worth going for, and partially because at this point in history, the Greenlanders really had to start looking after life and limb in Greenalnd and could not afford to waste resources on Vinland.
This is only my recollection of the story. The first caucasian child (that we know of for sure) to be born in Canada was a baby named Snorri. He grew up in Greenland. I suppose that hypothetically speaking, a child could have been left behind or stolen, but then that ought to be in the annals of Norse history, because they took very careful note of who was born, who died and so on. I do not know of any such notations, and I am sure there would have been at least one if a child would have been lost.
All that is besides the point that if a baby had been left there, no Noreman or -woman went back to Vinland at a time when such a child would have been an adult like in the movie.
Either way, I don't think the movie is meant to be historically accurate. It's just an action movie with an interesting storyline. If not, you don't need to pick the storyline apart for its historical accuracies - you could just look at how both the indians and the supposed vikings are dressed and how they behave. Neither and indian nore a viking would recognize their own culture the way it is depicted here. It's just a movie - emjoy it for what it is, the cool effects and such, and forget about vikings and indians.