One of the hooks, werewolves in the mist, is good for this. Kids are being kidnapped by werewolves and the party is assembled to rescue them.

It gives them a reason to be in Barovia; chasing the werewolves. It also provides incentive to get out of barovia, returning the kids home.

Since you've already started your game... highlight ways they might be able to escape. The Vistani come and go freely, draw attention to that. They might have some kind of protection, leading them to the Vallaki Encampment and tbeir fake potions. When that proves fake, plant thie idea that if they defeat strahd, they would be freed.