This may sound a bit on the wild side as your 4-yo doesn't appear to be affected; however, your 2-yo is and one of the main culprits could very easily be what you use to clean house and do laundry. My grandson is one of 4 and appears to be the only one affected in his house - also asthma and allergies. HOWEVER, when he is at my house for the summer, he doesn't need his 'drugs' and about the only difference between his house and mine are the cleaners I use and the fact that I also use an air purifier. Up until about 4 years I was totally ignorant of the many dangerous chemicals I was using thinking I was 'cleaning' my house - couldn't be further from the truth.
The following link is to a 30-minute very enlightening video and after that I'm giving you an additional link where you can check out the products you use to learn of their health hazards (if there are any).
To find out what’s lurking on your shelves, go to the National Institutes of Health Library of Medicine Household Products Database. You can search almost any brand of cleaner as well as personal care products you use, find out what’s in them, and uncover their links to health effects. Or search by chemical ingredients (see list below for some examples) and discover what brands contain it. The information may shock you. http://www.householdproducts.nlm.nih.gov/ingredients.htm
Chemical ingredients to look out for:
• Sodium hydroxide
• Hydrochloric acid
• Butyl cellosolve (2-Butoxyethanol)
• Bleach (sodium hypochlorite)
• Sulfamic acid
• Petroleum distillates
• Sulfuric acid
• Lye (potassium hydroxide)
If you have any questions, I would be happy to help guide you to a potentially healthier home and restful nights.