Thanks for the questions.
The assumption of your original question (How do the youth believe in God today?), assumes they have been catechized and told about Him by their parents. Sadly, we can't always assume they have been catechized correctly.
Many parents have been lapsed in their own faith, due to the lack of catechesis from their parents and the Church.
As Scott Hahn has said in his book, "Signs of Life":
For earthly or heavenly goals, our bodies need discipline. Our bodies must be subject to our reason — or the order will be reversed: our reason will soon be subject to our bodies [desires.]
Signs of Life, Page 178.
The latter is exactly what is happening in the sex-saturated United States today.
If people don't believe in God it is usually because:
- they have had a bad fatherly experience in their life, which they project or blame on God
- they were never told anything about Jesus and Catholic Christianity, or
- are not willing to sacrifice a "if it feels good, do it" lifestyle for one that prepares them for the next life which is eternal.
If they were never told anything about Christ and Catholic Christianity, from their view, their current earthly life is all there is to live for.
The end result is they become either a secularist or atheist.
We can help their disbelief by first forming our conscience with proper catechesis, then informing their conscience, telling them about Jesus and the one Church He founded on St. Peter and his successors and encouraging them to:
- look into Catholic Christianity or
- just step into the back of a Catholic Church once in a while to see what's there.
No one will ask for any membership card and we welcome everyone with open arms.
I hope this helps,