Late to the party.
If you ever do have damping off, yes, sprinkling cinnamon is a good cure.
Or you could make strong Chamomile tea (I use the tea bags), and once the tea is cold pour into a spray bottle and spray the seedlings once a week.
And for your original question about the garlic, yes lots of people do the garlic and swear it works. Crush 3-4 cloves of garlic into a quart of water, let it sit a while (like maybe overnight), strain and use as a spray.
If you ever do get damping off it's also a good idea to sterilize all containers and tools with a bleach solution.