Asthma is a condition of inflammation in the nasal passage along with swelling and production of extra mucus which results in difficulty breathing. Asthma and allergies both are genetic so if anyone in your family is affected, it is more likely to run into your child too.
A skin or a blood test is performed to see whether your child is affected with an allergy that can trigger asthmatic symptoms. It is very hard to recognize it's symptoms in toddlers and pre-schoolers as their bronchial tubes are quite small and narrow and having cold chest or other illness can lead to inflammation of these airways, making them even smaller.
It's symptoms are coughing specially at night, wheezing/whistling sound while sleeping, cold that settles in chest quite frequently. These should not be neglected as infants are quite small to express themselves.
There are medicines for treatment which Can be taken using inhaler with a holding chamber which directs the medicine directly into the lungs or through a nebulizer.
With right treatment even an affected child can sleep pleasantly without any whizzing sound.