I totally understand how you feel about your children searching for others with the same Catholic faith, wanting to talk to others about their faith and not able to find them.
You say that your eldest will be going to a University, hopefully there is a
Neuman Center on campus. Cardinal Neuman, a holy priest loved youth and felt a need to have catholic youth centers to assist students by offering daily Mass, faith filled programs, etc. Have your 18 yr old check into this program to see if it is available at that University. If it is not,
check out a Diocese Website for the nearest one.
Write back and let us know how everyone is doing.
In my prayers,