Drug violence, caused by its illegality, is the primary cause of the children trying to get across the border. Legalize drugs and take the violence out of them.
Not only that, but consider that criminals in Colorado (and I'm sure Washington as well, but I can't speak for that) still consider marijuana an illicit substance worthy of criminal acts to attain and sell. We used to have the street folk in Denver hustling pot. That was their income. Now, nobody buys pot from the thugs on Colfax, because they can just go into a store and buy it. As a result, that guy on the corner of Colfax and Logan that always relied on drugs to put some food in his mouth now has to resort to other means.
What is he experienced with and what does he know? Drugs. Instead of hustling on the corner, though, now he is looking at maybe robbing a dispensary ... because hey! All that pot is worth a lot of money!
We're coming full circle here soon. I enjoy having pot be legal. What I don't enjoy is the nonsense of "legalization will reduce crime." That's just not so, since those criminals still view drugs as their choice of income and will commit the same (or potentially worse) crimes in the name of drugs. However, with enough time, the "Invisible Hand" will make its way to illicit pot dealers and they will find their market is dried up.
Now, had it never been illegal in the first place, I'm guessing we wouldn't be seeing this problem to the extent we have. It's just that the goal of reducing crime by legalizing drugs is going to take long enough to have an effect that it shouldn't be what we consider the main point of drug legalization. Our children's children will see the benefit of reduced crime from legalization, but we certainly won't. Criminals have relied on illegal drugs for so long that they are not willing to accept legalization at face value. To them, it's still the profitable item they have always dealt and they will continue the same criminal acts to attain it as they have in the past.