Mix the cornstarch and glue together in a pot on medium heat on the stove. Once they are mixed well, stir in the baby oil and the vinegar (or lemon juice if that is what you are using).
Cook over low heat stirring no stop until the mixture resembles mashed potatoes. Then remove the pot from the heat and turn the stove off.
Sprinkle some cornstarch on your counter and rub some on your hands before removing the dough from the pot.
Place the dough mixture onto the counter and knead the dough until its nice and smooth. If your dough starts to stick add more cornstarch. You will know that the right amount of cornstarch is in it when it becomes smooth and clay like.
Once your air dry clay is done, shape the dough into what ever shape you would like. You can at this point roll it out with a rolling pin and have the kids make hand prints in it or have them shape it into animals or whatever else they want to create.
Once you have the shapes done, or the ornaments made, let the clay dry for two days. I leave our projects on the kitchen counter, you want them to be in an open space to dry out. After the 2 days drying time you can then paint the clay or leave it as is.