Indoor air can become highly polluted. They should try a top of the line air purifier in the bedroom at the very least. Even in the cold winter, the house should be aired out at least once daily and appropriate humiditiy levels maintained.

Keep the humidier CLEAN so it doesn't transmit mold spores or bacteria into the air.

Don't use fabric softeners or those little scented dryer sheets.

Don't spray aerosols in the house (hairspray, deodorant).

Don't use Swiffer dust cleaners.

Don't use nailpolish remover or other volatile organic chemicals in the house.

New carpet is a trigger for asthma. New foam products like a new couch can trigger an event.

Cockroaches in the house cause childhood asthma.

Check any daycare center they attend for what cleaning products they use.

Get the duct work in the house professionally cleaned for dust mites.

Fix any leaks in the plumbing, mold lives behind the walls where you can't see it.

STOP STOP STOP feeding them GMO food, go organic exclusively for awhile to see if symptoms revert.