A finger up the bum is often a good move.

These kids have got it right. Maximise your pleasure and that of the others with everything that's 'on hand'. 
Btw, that rubber johnny he's wearing, is that cum in it? If so it's not very much, but I don't think it is. I reckon his idea was to fuck one of them up the bum but got sidetracked. He can always do it later. He's sure as shit not gonna forget it, is he? 😄