A moment of silence or voluntary prayer would be in direct violation of the first amendment.The constitution was based on freedom of religion and even though the prayer would be voluntary,people who did not have the same beliefs would feel pressure to participate in the activity therefore violating their first amendment rights.
There is no need to amend the US Constitution in that manner. It would undermine religious freedom, and it would set a dangerous precedent that fundamental rights can be chipped away slowly. Such an amendment would not be able to garner the support to pass in all the states needed anyway.
No one will force children to pray or participate. Students might feel "pressured" into participating but no one will force children to pray. Students feel pressured into participating in drugs and drinking but are not being forced to. Additionally, this will give students a chance to learn about tolerance of other religions and lifestyles.