Well, If it was hot outside the day before it started raining, then you can say "Remember how hot it was yesterday? It will be a very nice change of temperature. Very cool and refreshing." Other examples of persuasive language could be "We can jump in the puddles for fun if you want, too!" Or, if they don't like that idea, you can always say "We can make a game out of dodging the puddles while we run, by jumping over them and running past them!"