some, not all, shower gels or shampoo have isopropyl alcohol as a constituent in them that can cause poisonous effects in children especially in ingested or aspirated.
this being alcohol is absorbed in the blood stream and may also cause aspiration of fumes into lung causing respiratory symptoms. especially if taken in large amount.
as you said your child is complaining of respiratory difficulty you should take your child to emergency to get him examined by a pediatrician
some tests that would be needed may be blood biochemistry, Blood gas analysis and Xray chest, ECG or any other test considered necessary for the child.
don't panic and be calm, as every thing should be alright with the right care.
wish your child rappid recovery and good health
Dr. Amit Kumar