At first, Serge will be reluctant on speaking with Shanoa, as he'll be very worried about his mother's whereabouts. Rescuing her will take all his sorrows away and let him become the playful kid he always was, allowing him to give quests to Shanoa.
During the first quest "Hide and Seek!", Serge will always be in a random barrel every time the quest is initiated, this requires speed and luck from the player, as there is no single way to determine where he is.
During the third quest "Can't Catch Me!", only Shanoa's surroundings will be pitch black. The second screen of the Nintendo DS (the one that shows the current map/enemy information) is still visible, making the quest quite easier than it would seem, as Serge is just on the roof of the building near where the player starts.