Here, diocesan Safe Environment regulations prohibit the presence of unsupervised minors. All children must be accompanied by a responsible parent or guardian at all times, even–especially–in the restroom during Mass, etc.
Any unsupervised minor showing up at church without parents would be sent straight home by someone in charge. How they would get home would be an interesting question.
This is awful and so far from the Gospel. What happened to: “Let all children come to me” which Jesus said to the apostles? What happened to reflecting the true love of Christ? (Matt 19:14). He wouldn´t send His children away, and neither should we.
Preventing minors (generally, teens) from going to church without their parents would be a great danger and thus we could easily make them feel unwelcome. I´m a teenager myself, although not a minor, and I´d say that if I were being treated like you present here, I´d honestly find it way easier to spend my time elsewhere.
Every since I converted at the age of 15 (I´m 18), I´ve been going a lot to Mass, adoration and confession on my own. And you know, the seal of confession applies to me too. My parents have no canonical right to even be aware of that I go to confession. And how are minors supposed to be given the necessary secrecy and privacy with regards to confession if they cannot even go to church by themselves.
The reason why I´m Catholic to this day consists in having found the Truth within the Catholic Church and realizing that God is here, in the Church. I would´ve never found God in the Church if I weren´t welcome, and if my longing for God weren´t considered just as important as anyone else.
We should REJOICE and be genuinely HAPPY for every single soul that seeks God voluntarily and with love. And that goes for our kids and teens as well. I´m honestly shocked of how someone could even want to question whether minors are to be welcome at church…! How disturbing and so far from the Gospel!