I provided the boys with pre-cut triangles which I cut from scraps of papers left from our other projects. For the 'flavours', they picked colorful papers and simply tear and paste for the collage. The more challenging part of this collage for the 2.5yo is to cover the gaps, which he did after a few reminders.
By the 4.5yo. Every cone was licked and partially eaten, hence so little ice-cream left in the cones.