I have a 18 month old dck and while she does attempt to use a spoon/fork the food has usually fallen off by the time she gets it to her mouth and just opts to use her fingers. Does this child at least use his fingers? just put the food on his tray and leave him. If he just looks at it put something in his hand and guide his hand to his mouth ... He'll get the picture pretty quick. Ask the parents to work with you at home by not feeding him unless it's yoghurt or similar.