Many kids with asthma need to take medicine every day to control their asthma. There's a good reason why should they take medicine even when they're feeling fine: Long-term control medicines work by keeping the airways in the lungs open and clear, which makes it easier to breathe.
These medicines work slow, not fast. It may take days or weeks for them to do their job. That's why a person with asthma needs to take them regularly. That gives these medicines a chance to get working, so they can keep airways from getting swollen and narrow.