If you have the cake and fruit, what about a trifle - the custard takes less than 10 minutes and that's dessert made. A fruit crumble - there are heaps of crumble alternatives, but here's one that you could try:
100g dark brown sugar
100g toasted hazelnuts
120g butter, cubed
70g rolled oats
70g plain flour
Place ingredients into clean dry TM bowl and with dial set to closed lid position, press Turbo button 2-3 times until crumble mixture forms. Sprinkle on top of fruit and bake for approximately 30-35 minutes until fruit is bubbly and fragrant.
Serve warm with plenty of whipped cream and/or ice cream.
Maybe a plate of brownies, but considering the time available and the fact that you are probably flat out running around getting your son ready, etc., there may not be time for that.
I've just noticed that Bron is on the forum at the moment, so she may have some ideas as well, but time is the factor here so fast and easy is what you are needing.