Gratman,
The headphone style that I highly recommend are made by Howard Leight (a Div of Bacou USA safety,Inc) and are called Leightning 31.
They are adjustable,padded amply for comfort and have a noise reduction rating of 31 Decibels. I have really enjoyed mine and never go to range without them. Picked them up at a well stocked sporting goods in my state and they were priced around $35-$40.
You can get cheaper ones with lower noise reduction ratings,but I highly recommend the extra investment for adequate protection and comfort. You won't regret it. Whatever you get, check to insure proper fit.
If all that is available are the lowed dBA rated HPhones, then added protection for your their ears would be to use a pair of the soft foam plugs in addition to the lower dBA type HPhones.
Your dear young shooters will surely remember your concern for their safety throughout their lives. Good thing you are doing, and best....Primer :wink: