Can aortic stenosis cause chest pain in a 5yo?

Rarely: Less than 10% of children with significant aortic stenosis have chest pain. Typically aortic stenosis is recognized by the presence of a heart murmur and intervention is undertaken before symptoms develop.

Yes but it's unusual: Aortic stenosis (as) is narrowing of the valve leading from the heart to the body, and usually causes no symptoms in children unless it is quite severe. In a small fraction of children, severe as can result in shortness of breath, fatigue, swelling, chest pain or fainting. However, most cases of chest pain in children are not caused by heart problems. A pediatric cardiologist can sort it out.