K.T.
My feeling is, first off depending on the child, I think 18mo old is too young for a time out, as you can see they think it is funny and they just dont get it. As far as the food, I would only give her a couple pieces on a plate, not her entire dinner, and if she throws it, get the plate back and give her a couple more pieces, if she does it again, I would NOT remove her from the chair/table, what I would do is, take her plate away and have her sit (in the highchair) at the table until you/ the family is done eating. Perhaps her seeing you and others sitting there eating civil and not throwing she will then get it. Dont let her have the easy way out and let her be excused just cause she threw her food!!! Let her sit there with nothing til you are done!! Best of Luck