I'll echo a couple of sentiments...
Unless you can offer expendable boxes that are off-
line, don't even think about this. And whatever you do,
don't offer a child a computer that work of the business
is actually performed on.
The legal problems are capable of completely wiping
out the company and possibly whole careers.
(including yours)
If a child accesses the worst aspects of the internet/
chat - You're in trouble, and possibly the child's life is at
risk.
If a child accesses files related to clients and throws
them away, corrupts or in any way disrupts the
commerce within the organization... do I need say
more?
If a child accesses sensitive personal information about
any employee... again, someone's gonna be sued.
The only viable solution would be computers that are
totally expendable that have no access to the outside
world.
Standard user level accounts would be prudent, with
appropriate age/grade level educational games/
software installed.
Be sure to follow standards for software installation.
Create a computer usage policy for these computers
and be sure to have the parents read & sign it! For
those children say age 12 and above, get them to sign
an additional "child's portion" usage policy.
This will help instill a sense of responsibility and
accountability.
Good luck... you ARE gonna' need it... along with
asbestos underwear, kevlar body armor and REALLY
good attorney.