Chukim and mishpatim are two kinds of mitzvot given in the Torah. A chok (decree) is something that man cannot understand and no reason is provided. A mishpat (judgement) has a logical reason behind it that man can understand. Rashi (Vaykira 18:4) gives eating pig and shatnez as examples of chukim and the law against stealing and murdering as examples of mishpatim.
I heard a simple way to describe this to children and tried it with our own. Here’s how the conversation went:
Abba: When you ask if we could go to the ice cream shop and I say “no”, what do you say?
Kids: We ask “why?”
Abba: When you are fighting with one another and I say “stop”, do you ever ask “why?”
Abba: Why don’t you ask “why”?
Kids: Because we know that you don’t want us to fight.
Abba: That is the difference between a chok and mishpat. For mitzvot that we don’t know the reason for, we may ask “why”, like when Abba says “No” to getting ice cream – that’s chok. For mitzvot that need no explanation because the reason is obvious, like not fighting with your siblings – that’s mishpat.
Try this explanation with your children and let us know how it goes.