What did the drummer boys in 17th and 18th century conflicts do when charging? Did they actually participate in the combat or did they just kinda awkwardly stand there and drum?

To clear up one big misconception, drummers in the 18th century were not always, or even usually, young boys. Musicians were paid better than private soldiers, and the head musician of a regiment, the drum major, was a non-commissioned officer. The drum major was also responsible for flogging offenders sentenced to receive that punishment, which was certainly not a job a child could physically perform.

Also remember that hand-to-hand combat, outside of surprise attacks made in the form of bayonet rushes, was pretty uncommon during the American Revolution. A bayonet charge almost always caused the side receiving the charge to retreat to a position where they could volley their muskets safely. Being that musicians stood at the back of the regiment anyway, they were thus unlikely to come into physical combat with the enemy, even when the rest of the regiment became so engaged.

Sources: Von Steuben's Blue Book.

Matthew Spring, With Zeal and With Bayonets Only