Yes, but you just have to make sure to supervise them the ENTIRE time and only let them swim for short periods. Afterwards, they have to get dry real quick so that they don’t chill.
I would not feed it chick starter, or layer mash. It’s not going to have enough niacin in it. I recommend ordering a duckling feed like the one Phantom mentioned which would be perfect for it. Or if you can’t find duck specific feed, purchase some flock raiser crumbles. They have that stuff...