What you are witnessing is the extinguishing of the fire of the divine life in their souls from starvation of its natural food supply - the Most Holy Eucharist.
How very sad!
The very young you speak of are enthused because they still have the habits of faith and charity.
It is very sad. It is also disheartening to witness first hand the slow extinguishing of the enthusiasm and faith and charity. I pray for all my students and hope.