Singulair and tiny things

My two sons have been taking Singulair off and on for allergy symptoms. Recently, I noticed this was causing both of them some side effects. With my youngest son, I noticed some serious mood swings and just discussed this a couple of weeks ago with a close friend. I told her what I thought was causing his mood changes, stomach aches, and etc. I experienced some over the weekend because my son was given this medication by mother that had some at her house just in case one of them needed the medication for asthma or allergies. I hadn't discussed this with my parents because I was logging this in a notebook, and I was confirming some things before I told anybody else what I thought about Singulair. Guess what? It happened again because it was administered to my youngest son by my mother not knowing my concerns. I didn't tell her because they went over late that evening then coming back in the morning. I wished I would have told her. Although, she feels very badly because I did tell her about my concerns after she had told me she had given this Singulair to him. This was after I had told her he was a a major mood swing!!!! Outrageous!!!!!!!!!!!!!!!!!!! My oldest son has experience major headaches, biting my husband and my head off over tiny things. (Thought it was the teenage thing.) I will not be giving my children SINGULAIR>>>>>>>>>>>>>>>