If I gave you a ducky towel for the birth of your child, it’s alright to use it for your other children as well. Children of all ages enjoy the ducky towels. I say they are for birth to 3 years, but that’s just an estimate of size. Really a newborn would be swimming in a ducky towel. And my 5 year old still uses the ducky towel—and he has a sizeable head.
I wash my yellow ducky towels on warm or hot and tumble dry medium. The bright blue or bright pink ones I'd recommend washing on cold so they don't fade too fast over time. The pale blue ones you could probably wash on warm or hot with no fading problems. I despise stinky moldy towels. Don't let your towels get moldy. Once moldy, you'd have to bleach them to kill the mold. Duckies don't like to be bleached. So make sure when your ducky towel is hanging dry that it's not all folded while hanging dry.