By the time the birds show signs that they have worms they will have a very heavy load. It can do permanent damage to the birds.
One of the things that Wes got me to try was Eprinex pour on for cattle & hogs. I love the stuff because its simple to use and I don't have to make certain my birds are drinking it. The other thing he recommends is that there also be a worming for round worms, Eprinex does not take care of round worms, using Wazine.
Right now I'm using the Eprinex in the late Winter and the Wazine in the late Summer. That is subject to change if I see anything going on.
My second recommendation is taking a couple fecals to the vet. That way you will know for certainty what, if anything, you need to treat for.