When we speak we always breathe out continuously. Or when we sing.
And I use a spring of water as an image. Interrupted by my finger as an illustration of the tongue. But there is one thing that we as teachers cannot explain completely or I cannot. How to use the tongue? Soft Ta? da, la, ga, ka, tha... I was about to say Lady Gaga.

I don't think there is any easy way to teach legato but a little humor can help the young people. But one way I have used is that they sing first and then play. On strings you can see what is happening, but with us we can't see what is happening. inside the mouth. The bow is both air and articulation.
I now have two students aged 12 who play bass and tenor. They are not quite ready for bordogni. So i use f-f-f-f-Eb legato. Sing first. Then I use melodies like «twinkle twinkle little star»
For some it takes years to learn legato, me included.(Still strugling) But Im happy for advice how to teach!
Leif