Good Morning JingleBell
All medicines may cause side effects, but many people using Singulair chewables have no, or minor, side effects. Check with your doctor if any of these most common side effects persist or become bothersome:
Cough; dizziness; headache; indigestion; nausea; stomach upset or pain; stuffy nose; tiredness; trouble sleeping; weakness.
I am glad you are going to call you child's physician. Please keep us posted on how things are going for your child.