Make the bilingual children your co-teachers. When the other children have to work on their own or in small groups, for example, the bilingual children can go round and help them. You can prepare the next task in the meantime. Or ask them to explain certain grammar exceptions or idioms to the class.
Whenever you start a new topic, you could ask them beforehand if they like to prepare some additional information for the class. Thus, they will be busy during lessons without getting bored. They will thank you these tasks with little disruptions and good behavior during lessons.
Make them feel special. They are special and they should be proud of it. However, watch out for them starting to show off or pick on other children. If they do, you have to stop that at once. They are special but not superior to others only because they speak more languages.
You see, bilingual children can be a great enrichment to your language class but they can become a problem too if they start to feel superior to others. A healthy balance between assigning them special tasks and treating them the same way as their classmates may be difficult to attain but is essential.