Can I sue an ex for slander?

If your ex tells your toddler aged kids bad stuff about you all the time, has them call and say "you're not my dad", teaches them that their last name is their stepdad's and not their yours when you are their father and you have custody and their legal name is yours, teaches them to call you by your first name and calls you an and all kinds of names on facebook... Can you sue for slander? What else can you do legally?