Hi DuckTuckandRole, that is really exciting that you're raising baby mallards! I'm 14 too and I have always been crazy about birds and other animals ever since I was a baby (duck was my first word.) I have kept all sorts of animals and bugs as pets and have rescued quite a few too. If you want to know about them just let me know
I don't have any ducks now but I'm hoping to get some ducklings and baby chickens soon (I'm sooo excited!) Mallards have always been my favorite because a mother mallard laid an egg and left it at my grandparents house in the back yard while we were visiting. I tried to hatch the egg under a lamp, but the baby never hatched and we found out that the red ring meant that the baby bird died early on (I didn't know then that it had to be a certain temperature.) Mallards are also beautiful birds and really cute babies
I have done a lot of research on them since then and I will try my best to answer your question. If you really want your mallards to fly south for the winter they would need to follow another mallard that has flown south before, because in the wild they follow their parents, so the next time they will fly the same route and later show their babies how to get there.
You could take them to a pond that has other mallards so yours will follow them when they fly south. When it gets warm again they should come back. Just make sure that the wild mallards live at the pond, because they will return to the place they were born. If they live there, there would probably be a lot of them. If you don't live near a pond that has mallards, then the best place to keep them is in your garage, or an outside pen with hay to keep them warm if your mom doesn't want them in the garage. I think duckling diapers would get expensive and you would be exhausted changing them all the time.
If you decide to keep them for the winter, and you don't want them flying off and getting lost when they are let outside, then their wings will need to be clipped. They still have the instinct to fly off even though they have no idea where they are going. I hope this helps, and let me know if you have any questions
~Destiny