I've given youngsters a start a couple of times and what I've noticed is they have a complete inability to think for themselves. I wouldn't expect anyone (with no experience)to pile straight in and know what to do, but I've found that unless you are telling them what to at all times they just stop and wait to be told.
It becomes very hard work thinking for them as well. I'm not talking about mentally demanding work either just general labouring. They just seem to lack motivation. All you want is someone to say whats next or to look round and tidy up or just show a general interest.
I don't think for a minute that every single youngster is like that, but I do think they are mollycoddled a lot more in school and this shows up in the working world. I really fear for the construction industry in the coming years.