From the readings so far, I don't think you can "match" the amount as you described. - If the kid earned $1,000, the most amount the kid can contribute to Roth IRA is $1,000 minus self employment tax (about 20%-ish). You can't give him another $1,000 as "match" to make his total as $2,000 (minus self employment tax).
Wherever you see "match", it means that, for example, kid earned $1,000 but used all that money and bought ice-cream and ate all of them. But now he wants to contribute to Roth IRA but he has no money now. My understanding is that under this case, you can give ("match") him $1,000 for this goal. Basically his total contribution can't exceed his total earning.
