Hello and Welcome To BYC! Pretty flock! You can post questions about your ducks on the Duck forum, if they are still pretty young it is probably just an age thing www.backyardchickens.com/f/42/ducks
Adorable flock! Yes, chicks and ducklings don't get their adult voices until they are fairly mature. So give them time. Kelsie has left you with the link to the Duck section if you have any questions on raising your ducks.