Can exposure to diesel fumes while traveling in a vehicle daily cause cancer? i worry about my child as our daily commutes are very long?

Diesel exhaust is quite toxic and prolonged or intense exposure might raise cancer risk, but the main problems are respiratory and cardiovascular. Exposure on roads and highways is not usually very dense except in heavy truck traffic. Actual risk for most individuals probably is very low from normal daily life. Google "diesel and health" or similar terms for lots of information.