Nice idea! I usually cut an avocado into little cubes for my little girl, with a sprinkle of lemon juice, salt and garlic powder...I bet she would love it as a dressing to mask any foods that she doesn't like!
Avocado salad dressing
I only tried making this once so I don't really know the exact measurements, but all you need is an avocado, a lemon, water and a food processor. You can try using half an avocado. Maybe 2 tablespoons of water. I would recommend not using the whole lemon otherwise it's probably going to be a little too sour, so maybe half a lemon depending on how sour you want it to be. Throw the half of an avocado, half of a lemon and 2 tablespoons of water into a food processor and that's it! It's a nice dressing, more on the thick side so it doesn't all drip off the lettuce onto the bottom of your bowl. I really think it's good just with the avocado, lemon and water, but you can definitely throw whatever else you want in there and I'm sure it'll turn out great! 
