We are fairly new to ducks ourselves! We had them when I was a young child, but of course, didn't remember a thing about actually taking care of them. I will say that if I do babies again, I will not do it in the winter because we have to keep them in so long! Too cold! I love them, but it is such a mess having them in the house for that many weeks.
Anyway, if you can, I would definitely try to get another duckling - they really don't like to be alone and will probably cry a lot. In the meantime, adding a towel or old stuffed animal can help. Just prepared to change it out or wash it now and then as she/he will poop everywhere. We had a single duckling for about 2 weeks because the others we ordered with her didn't survive. We found that adding something soft helped her to not be quite as lonely until the other 3 arrived.
If you absolutely cannot add anymore ducks as someone else suggested (1 adult to the adult duck and another duckling to the current duckling), then it would be best to rig something up so that they can see, smell each other, etc. I wouldn't put the adult with the duckling as it's likely to hurt it at this point. I even had trouble with my 2 week old beating up on the brand newly hatched ones when they arrived and had to slowly introduce them.
My ducks are now just about to reach 8 weeks of age and they are outside all day with temperatures ranging from 30-60 over the past few weeks, but they are still inside at night because we are dropping into the teens and a couple of them are still working on their feathers. I plan on putting them out full-time in about 2-3 weeks. They are currently living in the bathtub with straw at night, which is sooo much fun to clean out every morning. NOT! : ) But, I would rather wait until I know they can handle those low winter temps before I put them out. They grow fast! I basically have 4 adult ducks in my bathtub, no more duckling size!
I tell you this to help you be prepared that you will have a lot of cleaning to do for a while before they can go out. Of course, if you end up getting another adult duck, the two adults can go out - but the baby will be with you for a while yet.
One thing that is very important is to get niacin for your duckling. I had to get mine from our health food store because none of the other stores carried regular niacin - don't get the "time release" or "no flush" kind. I get mine in 100mg capsules that I break open and dissolve in a gallon jug - 100 mg to a gallon of water. Give her/him this water for her drinking water all the time.
Other than that, have fun with your new additions! If you get an old towel that you don't mind the duckling soiling, he/she will love to sit on your lap and sleep. Mine would even jump onto my lap if I was sitting on the floor and patted my leg and called her.
I've learned a lot on here about raising ducklings and the rest has been by trial and error. Feel free to ask as many questions as you need!
