Bird sitting

Every year, sparrows nest in a small opening on my front porch. And, every year, at least one baby falls out. Last year, the baby survived the fall, and had the start of feathers... I fed it until it was big enough to fly away...
This year, the first baby was too little to make it... but we have one now that we are feeding, and is almost ready to fly...
You just don't realize how much work feeding a baby bird is. He (I call it a he, I really can't tell until all his feathers come in) eats every 20 minutes or so, at least 16 hours a day. I always have to make sure that someone is here to "bird sit" when I'm out...we have unflatteringly named him "The Mouth", LOL.
I suppose some of you may think this is a lot of unneccessary work... I should just let nature take its course... but I really can't see letting these tiny birds die just because their parents have a lousy nesting spot. I know I can't save them all, but I think I have an obligation to at least try to save them...