A member of my family has been involved with YWAM for a number of years. This group targets kids who truly want to work for Christ, isolates them far from their families and home churches, and convinces them that they are "missionaries" doing important work for God.
Once people are hooked, YWAM then preys on them financially. The kids themselves have to raise the money to pay for their training and supposed mission work.
Imagine never hearing from from your loved one again except in the form of letters requesting "love offerings" to fund their umpteenth Discipleship Training School (DTS) or "missionary" trip. YWAM also encourages kids to recruit their friends and family members to join. Voila, more people paying for DTS. What a scam.
To people whose kids want to join YWAM, I would say, Guess what, you can do God's work at home, in your own town, and not have to pay a hot red cent. And if your child has a calling to be a missionary, send them to an accredited Christian college where they can get real, long-term training for this job.