A way to enforce Safe Search for Google, Bing, DuckDuckGo, YouTube, Qwant and Pixabay w/o editing dnsmasq config files.
Add the custom.list file in this repo to /etc/pihole/ as custom.list by running the follow line.
sudo wget https://raw.githubusercontent.com/ajp2k13/custom.list/master/custom.list -O /etc/pihole/custom.list
then restart the pihole-FTL service for the changes to be active.
sudo service pihole-FTL restart
you might also have to flush the dns cache on the devices using Pi-hole.