But no. Clearly this is ensconced tradition. With a single exception where the grandmother made sure we were all offered cake to eat at the birthday party itself, Grouting has consistently been sent away from her cohort's parties with cake wrapped in a paper napkin.
I knew about being sent off with slices of fruit cake from weddings, but fruit cake lasts in a way that sponge - especially iced sponge which sticks to paper napkins - does not. Marzipan holds up better than the frequently-encountered buttercream on birthday cakes.
This is a baffling tradition to someone who'd rather just eat the cake at the party when it's fresh. Unless a gift bag with bonus paper+cake is excavated promptly, it goes rapidly stale, and is already sticky. And it's really easy to forgot to do it promptly if, for whatever reason, one's offspring is not inclined to lead the way on doing so that particular day.
How long as this been a tradition in England or further afield? And WHY?