First, I have to start with the fact that my husband is one of the people that chooses and pays certain online celebrities and/or people with big followings to do product placements for the giant corps. They make a shit load of money (the online peeps) through this alone. You might have seen my recent posting about the emailing boss from hell.
There are 'agencies' that represent people such as this family in their dealings.
Next, you have to realize that for every family making videos there are 100,000+ families WORLDWIDE, that are not making the videos and creating content- they are just watching them (out of boredom, between things, etc). This is why it is unique and valuable, for now. Of course, the market is about to be flooded with people doing this exact thing, because it is easy and becoming well known. They just happened to be one of the first to do it.
These people are creating assets which results in residual income. The videos will continue to earn them big bucks for a while even if they never uploaded another.
And yes the woman on youtube started uploading the unwrapping toys 3 years ago (one of the first to execute the concept) and makes $5,000,000 a year off the views. My toddler loves her videos (think kids watching a birthday boy or girl unwrap their presents).
My son is a huge fan of Stampy (minecraft video creator). Stampy makes a high income uploading one 30 min video a day of himself playing the game. This has inspired my son to make videos on his own (the fun of it, not the income part).
The world's a-changing.