Congratulations. You're in for lots of fun and the kids will enjoy it too. I have to agree with Corgi1 however. The chain tensioner should be on the bottom of the chain. Tensioning the top really doesn't do anything. If it runs okay like you have it you can probably do away with the tensioner altogether. Just shorten the chain and use your dropouts for tension adjustment if you have adjustable dropouts. Good luck, ride safe.
Tom