I have twins and they were diagnosed with RAD (reactive airway disease) @ 10 mo old. We started pulmicort nebulizer treatments then. We did them twice a day and even a third time if they got a cold. DD would go from a slight cough to coughing every 2 min within a 24 hours if she got a cold. We would have to give oral predinsone too frequently for our pedi. He referred us to an asthma/allergist.
DS and DD started seeing her around 2.5 years old. She added singulair daily. It did help quite a bit. We also give zyrtec daily year round. DS's sinuses get yucky and DD's nose runs incessantly without it. She also did skin patch testing on them around age 4. They were only allergic to alertnaria mold.
I don't remember when the diagnosis changed from RAD to asthma, but it was at least by 2.5 yrs old. They kids are almost 9 (!) and DS no longer uses a daily inhaler and is doing well. We will try to drop the singulair soon. DD uses her inhaler only 1 puff once a day and doing well. Thankfully, the kids have never had to visit the ER or be hospitalized due to their asthma.
ETA: wrong word