I'm taking it (with Sionned) that this is EFL?
I have a lot of sympathy for the attempts to build structures that let people teach English/etc without using the local language/s - but it just can't work as well as making the effort to learn enough of the local language/s to start from a base of real understanding for some key vocab/structures.
But hey. For maximum ease of the initial 'guess what I'm doing' presentation, I'd recommend rhedeg, cysgu, dawnsio, neidio and eistedd. Act these with just the verbs themselves. Then, with the aid of plenty of pointing, get them to echo, so when you say 'Dwi'n rhedeg' (pointing at yourself), they answer by pointing at you and saying 'Ti'n rhedeg!'. Run through the five two or three times quickly like that - then start pointing at random individuals and saying 'Ti'n cysgu!' until they get that they're meant to do some acting - then encourage them (it's just a reverse of the echoing, so most of them should pick up on it quite quickly) to say 'Dwi'n cysgu!' after you've pointed at them and said 'Ti'n cysgu!'.
Then get the brightest of them to come up and take your part, while you go sit in the audience and help lead the 'Ti'n rhedeg!' responses.
Then get a pair of them up to the front, and get them swapping 'Dwi'ns' and 'Ti'ns'. Then get the rest of them into pairs (point at the pair at the front, try holding up one finger on your right hand and one on your left and then bringing them together) and let it all descend briefly into a riot of bad acting and random shouting.
Then clap and point until they're all sitting down and quiet, do 'Dwi'n rhedeg' with minimum acting, make a 'you all' circle gesture and an 'on your feet' palms up gesture, and then try and get them saying 'Dwi'n rhedeg' with you (laugh and shake your head at the inevitable 'Ti'n rhedegs', and do a bit of 'Dwi'n rhedeg', 'you all' gesture and lead the 'Dwi'n rhedeg').
Once they've got the idea that they're meant to say what they're doing, run through the five verbs on a you/them basis, and then clap, bow, and sit down firmly.
Oh, and offer up a silent prayer of gratitude that we don't try and teach you like this with SSiW...

Pob lwc!