No. L-2 child status does not authorize employment.
Check the helper’s status, not the usefulness of the task
Permission to work is decided person by person, never by how useful the task is or by who is willing to pay for it. A child admitted in L-2 may attend school full time, but that status carries no work authorisation, so paying them for translation would be employment they cannot lawfully accept, and the fact that the work supports a parent's petition changes nothing. The spouse sits differently: a qualifying L-2 spouse is employment-authorized incident to that status, so the ability to take paid work comes from the spouse's own maintained status rather than from the principal's assignment.
Age matters as well. Dependent child status ends at twenty-one, so a household relying on a teenager's help across a multi-year assignment should count those years before the transfer begins rather than after it. If the translation genuinely needs doing, the workable answers are to have the company do it, to engage an outside vendor, or to use someone who already holds work permission in their own right.
Where a relative's own plan is to work or study on a different basis, treat that as its own question, with its own evidence and its own timing. Derivative status is also only as sound as the principal's, which still rests on a qualifying parent, branch, subsidiary or affiliate relationship between two actively trading entities, one continuous year of qualifying employment abroad within the preceding three years, and knowledge that is special to this organisation or advanced knowledge of its processes rather than general trade skill; where the work sits at an unaffiliated client's site the petitioner must keep control of it and the placement must not be labour for hire.