Screaming toddlers at daycare?

Toddlers are at an age where they are trying to be "big kids" but don't really know how. They have feelings and wants but don't necessarily know how to express what they want. They are also learning that they have some control over their environment and body and they have learned screaming works. This gets them a reaction and attention.
If you know why the toddler is screaming (for example, another child took their toy) you need to give them the words they need. At first it will just be you saying it "Say, "No. I don't like that". Eventually you can make them repeat after you if they are capable, and down the line you may be able to just give reminders to "use your words".
Toddlers are also trying to get a handle on their emotion. If you know that they are angry or upset give them the words to describe what they are feeling. It will start with saying things like, "I see that you are very mad. It's okay to be mad. Let me know when you're ready and I'll give you a hug" or something like that.