My dd2 has asthma, though very rarely does she actually suffer with it. She has been on ventilators twice, as a toddler (she is now 6) because when it comes on, it comes on bad. She only gets wheezy when she has a cold (no allergies).
Now, she hasnt really had an attack in about 2 years, so my memory is hazy. At what point do you worry and take them to a Dr or even to an A&E department?