Hmmm - more difficult with this age - but the answer is always the same - MOVEMENT!!!
Tap, clap, click, sway, nod, walk, pass an object...
For this age I would suggest that one of the most helpful things might be ball-bouncing! Teach different patterns for different metres - BOUNCE, catch for 2/4 (or 6/8), BOUNCE, catch (in one hand), pass (to the other hand) for 3/4 (9/8) and BOUNCE, catch, pass, pass for 4/4 (12/8). Once you've taught the basic 2/4 it might be good to ask him to invent his own ideas for 2 and 3 time before you give him these ideas.
Also walking the pulse. Get him to walk in time with your playing and then add other aspects - eg clap on every strong beat (or jump, or tap your head, or bend your knee, etc) - or to clap the subdivisions of the beat - ie walk crotchets, clap quavers (or walk dotted crotchets and clap quavers for compound time). Then try it the other way round (MUCH harder!).
Or - conducting! This can either be as in beating a different arm pattern for each metre, or just performing a different movement on each beat of the bar. These ideas are all Dalcroze-inspired and I know they have specific 'conducting' movements but I can't remember what they are...sorry
Hope this helps a bit!