What I did is that I forced everybody to get through OpenDNS, then I've whitelisted the stations that I didn't want to be using OpenDNS and replaced their preferred DNS by pushing the GoogleDNS with DHCP option 6.
If you want to restrict everybody except some stations, be sure to whilelist devices like Bluray players, XBox, Audio amplifiers, IP-Phones, NAS and all other IoT-alike devices otherwise you might end up having problems with them.
Then I've created hostnames for Google and Youtube to force them in to "low restricted mode". My technique is not perfect, but it get most of the job done. Here are the hostnames that I've forced:
Click to show list
www.google.ca ==> 216.239.38.120
www.google.com ==> 216.239.38.120
android.googleapis.com ==> 216.239.38.120
android.clients.google.com ==> 216.239.38.120
www.googleapis.com ==> 216.239.38.120
www.google.fr ==> 216.239.38.120
youtubei.googleapis.com ==> 216.239.38.119
m.youtube.com ==> 216.239.38.119
www.youtube.com ==> 216.239.38.119
www.youtube-nocookie.com ==> 216.239.38.119
youtube.googleapis.com ==> 216.239.38.119
For Youtube, I prefer using 216.239.38.119 (restrictmoderate.youtube.com) because 216.239.38.120 (restrict.youtube.com) just block too many videos, even appropriate ones.
I've followed the following guide, but I used the "reverse behaviour, i.e. all devices use OpenDNS except the ones you tag" method (see replies on the main post):
I have to admit that it looks harder than it is 
, and it might not fit your definition of "easy"...