Q.What is wrong with our viburnum trees
(see attached photo)
Your shrubs have an infestation that is causing leaf curl.
You can inspect the leaves and plant to make an identification.
Neem Oil is a good treatment and will take care of most insect issues.
Neem Oil is safe for people, pets and bees!
Here are some links with more information.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/ornamental/shrubs/viburnum/viburnum-shrub.htm
http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2057.html