The theme of connection could be present. Through the tickling, Minato and Naruto are physically and emotionally connected. It can also symbolize the connection between Naruto's past (represented by Minato) and his present. And perhaps there's a theme of legacy, as Minato's loving actions towards Naruto are part of the legacy he leaves behind for his son.
One possible theme is family love. The act of Minato tickling Naruto shows the strong bond between father and son, emphasizing the love and care within a family. Another theme could be innocence. It portrays the simple joys of childhood, like the innocent laughter that comes from being tickled by a parent.