The skinny one

In a poll of children by a toy manufacturer, getting toys out of tough packaging and checking the wardrobe for monsters are amongst the most prized ‘dad skills’. But the ability to fix what came top of the list? To find out, solve the puzzle… Add a letter anywhere in each of the boxed-off words to fit the clue, eg, PONDER = THIN + K = THINK. Write the added letter in the space provided. Read down the added letters to spell out the answer.