Going thru a divorce. Kids, girls (ages 5 - 13) are with mum. She feeds them bad information about me, Dad.?

How i'm such a useless guy, etc etc. Do i need to defend myself/respond to these allegations when i'm with the kids? What will be the effect on the kids if i tell them their mum lies to them? How do i protect myself from all the indoctrination that their mum is systematically implanting in their minds against me. How do i keep my relationship with the kids on a sure footing till they grow up and discover facts themselves?