Instead of drapes and cloth-covered furniture, use washable curtains or vinyl shades and furniture you can wipe with a damp cloth, especially in your child's bedroom. Wash sheets, blankets and pillows, throw rugs and stuffed animals often, using hot water to kill dust mites. Use pillows or comforters filled with polyester instead of feathers. Use cotton or acrylic blankets that can be machine washed. Don't use wool blankets unless they can be machine washed.
Dust mites and mold grow best in damp areas.
You may have to use a dehumidifier or an air conditioner to keep the humidity low. Wipe bathroom surfaces with a solution of bleach and water, and use bleach to clean in the basement and other damp areas to reduce mold and mildew. Try to keep fresh air flowing into these areas, and use a dehumidifier to keep the air dry. Try not to have pets with fur or feathers, or at least keep them out of your child's bedroom. Keep your child's bedroom windows closed to keep pollen out.