A report by the inspection agency Estyn, commissioned by the Assembly government, found that the current curriculum does not offer adequate support for outreach workers, counsellors, health officers or people carrying out extended curriculum work in schools.
And bilingual and Welsh-medium youth support is out of the question because the system is not delivering enough trained staff.
The report focused on the initial training courses that lead to a youth work qualification at foundation level. Inspectors interviewed staff, trainees, tutors and managers from nine youth services, as well as observing some sessions.
They found that the focus on youth clubs had deterred workers from other youth services from joining the courses. Now Estyn has urged course providers to broaden the curriculum. The agency also wants course providers to increase bilingual and Welsh-medium training opportunities.
While many courses offer students the opportunity to use Welsh-language materials, few take up the opportunity.
"There are not enough trained people to deliver bilingual and Welsh-medium youth support services," said the report.
Meirion Prys Jones, chief executive of the Welsh Language Board, said:
"It's important that the Assembly government has a clear strategy on how to provide enough bilingual trainers for this important field."
The report also criticised pass rates which lurched from 65 per cent in some areas to 100 per cent in others, and said there was not enough emphasis on key Assembly government policies.
Estyn also said there were too few suitably trained and qualified staff to act as work-based supervisors. As a result there are not enough good-quality placements available for fieldwork practice.
But the inspectors said that many youth services across Wales work well together to organise the training. These arrangements provide a wider base of work experience, reduce costs between the services and give trainees greater choice about which course to join.
An Assembly spokesperson said: "We are committed to high-quality training for youth workers and have made pound;1 million available from 2005-7 to support this."