My 3-year old daughter just took her first and last Singulair today. Within 3 hours: crazy mood swings for no reason, uncontrolled anger, bad dreams during her nap time. I didn't recognize her. She's been on Zyrtec for 2 weeks and showed improvement with her allergies and no side effects, but for some reason I let the doctor talk me into trying Singular today. I just threw the Singular in the garbage. Back to Zyrtec tomorrow.