So I came up with this. I did leave it to the last minute to bake and throw together, so here's what I did in 2 hours (including baking time):-
1 chocolate and 1 vanilla cake with strawberry swirls.
I went with Orchard Icing. I bought two packs, but should have gone with three. I was so rusty on my cake decorating skills!!
I didn't have any colouring paste, so I had to make do with some extra icing sugar and liquid colour. It worked just as well.
I cut the cakes like this...
To get this. Lego pieces! You do need to brush the cakes with runny jam (for vanilla ones) and a chocolatey drinking powder mix for chocolate cakes otherwise the icing doesn't stick. I was really lazy with the yellow and red blocks and didn't do that. Silly me - I should have known better! But I did with the blue cake (a chocolate one) and it was so much easier.
I used the screw on end of a piping nozzle (not the actual nozzles themselves though) to cut out the circles. I guess it looked like a mini scone cutter.
If I was more patient, I would have let the cakes sit for a bit more, smoothed the icing out more, and possibly allowed some more time (not to mention the jam!!) but I had to get the kids from school and then it was on.
Needless to say, my son loved it anyway :D