Four balls into the 22nd over, Kareem scored the final two runs for victory. The youngster, who also starred at this competition last year, also took two wickets with the ball for eight runs off 5.2 overs.
Sally Wenham managed two fine catches in the second innings for CD.
Earlier in the week, CD and Auckland looked to be the finalists with both sides unbeaten until they met on Wednesday.
Auckland easily accounted for the defending champions in the first encounter, setting the scene for yesterday's outcome in the final.
The Wanganui Festival of Cricket continues next week with the national under-13 girls' tournament from Monday to Thursday, while the under-13 boys' competition will run over two days at the end of next week.