Your character owns a useful item that he has practiced with for many a long hour. As such, the item provides an equipment bonus (see p. 132) beyond what such an item would usually provide, simply due to the familiarity. The item provides a +2 bonus to applicable rolls within its intended function (a harmonica provides the bonus to Expression rolls to play it, while a laptop computer provides the bonus to Computer rolls) and a +1 bonus to rolls a bit outside or related to the usual purview (using the harmonica to wedge open a door or using the laptop for a Study roll to get homework done on time).
Combat rolls can benefit from this Merit, but the Storyteller and the player should consider why the child has spent that much time fighting.
Drawback: If the item is broken or lost, this Merit is forfeited.