I'm actually shocked that Kagi doesn't support this yet. My scenario is that I use cleanbrowsing.org on my daughter's laptop. It does a good job of blocking most anything I can think of. But it also blocks Kagi. This thread at least taught me that duckduckgo is an alternative option for me now.
To be clear, we're not just looking for a way to do safe web-searches - Kagi does a good job of filtering results to a safe level - it's about having a good way to block direct access to, say, porn sites (which is what cleanbrowsing's DNS settings do) and also at the same time being able to use Kagi as search engine of choice.