Words translate problem
it's the best ways to keep them from turning into full-blown disorders.

1. Does full-blown disorders means very harmful/serious problem?

Many hitherto unobserved youngsters may have psychological problems

hitherto = by now /so far

I only know Many + people + unobserved..................hitherto.

2. why many + adv ?

Question

Words translate problem
it's the best ways to keep them from turning into full-blown disorders.

1. Does full-blown disorders means very harmful/serious problem?

Many hitherto unobserved youngsters may have psychological problems

hitherto = by now /so far

I only know Many + people + unobserved..................hitherto.

2.  why many + adv  ?

Answer

I can offer my thoughts:

"full-blown" means "fully-developed", so a "full-blown disorder" is a disorder (for example an illness, or a problematic behaviour) that is fully expressed - but it doesn't necessarily mean that it is very harmful (that would depend on the disorder).  For example, you might be anxious about some things without having a full-blown anxiety disorder.  In this context, a 'full-blown disorder' refers to something that is much more significant, and possibly diagnosed, or meeting all of the criteria for diagnosis.