You can propagate most succulents from a leaf, however some will require cuttings. The easiest way to determine which ones can be propagated from a leaf is to remove a leaf and test the theory!
Here we go - to propagate from a leaf, gently twist the leaf off of the stem. I’ve found that it has to be a clean pull, meaning nothing gets left on the stem. If you get some of the stem that is fine too. I had a few that ripped off just before the stem and all of those died. So, try to get all the way to the stem. It helps if you can see the end of the leaf as you are pulling it off.
Once you have the leaf you will need let it dry out a little bit before you do anything else. Depending on the amount of heat and sunlight you give the cuttings this could be 1-3 days. If you don’t let the end of the cutting dry up and 'scab over' it will absorb too much water and will die when you water it.
What I have found works best for the leaves is to place them on top of the soil (the end should be visible and not covered) and water them when the soil is dry. I use a spray bottle to get the top of the soil wet, although they are babies, they are still succulents which don't like much water at all.
Keep the roots covered as the plants begin to grow. If you don’t cover them with soil, eventually they begin to dry out and it’s hard to help them keep growing. Just remember it will take several months for the succulents to grow full size - but it is more than worth the wait :)