Question to anyone who can suggest.....
 

I am handling primary school kids in their third year of school English (ESL): their native languages are too far from English to use as a reference. A common mistake they make is the confusion (common, alas, amongst native speakers as well) between the possessive "its" and the abbreviation "it's" for "it is": i.e., they use the latter for the former. Any good exercises or not-so-dry explanations that anyone can suggest? I need it within the next couple of days. Thanks.