Even 18 month olds can learn that if they leave the table, the food gets taken away and no amount of screaming will bring it back...snack is in 2 hours.

This worked a charm for me with all of the many kids I nannied and I had little darlings that knew that when they were done they would take their plate to the sink. If they chose to walk off after 3 mouthfuls, the plate would be taken away and it rarely took more than 2 'shocks' to have the lesson very well learnt.

Good luck,
A