Singulair and term damage

Our 7 year old son has been old singulair since he was about 3. I can't even describe in words how I feel as a parent knowing now what my son has been going through. He (just like the others) has been very emotional and become very timid and has had a couple of panic attacks. I really began noticing it when his doctor bumped up his dose several months ago. He began talking about death and morbid things quite frequently. His doctor also has diagnosed him with ADHD. Over the past several months I took him to the doctor for extreme leg pain and once to the emergency room for crippling abdominal pain. They couldn't find anything wrong with him. We've taken him OFF of singulair forever and few days ago and him bright and positive personality seems like is beginning to come back. I just hope that he has suffered long-term damage from taking this medicine. At this point, we can only hope and pray that everything will be fine.