Should I get involved in this parenting issue?

A friend is divorced. I'm friends with him, my niece is friends with her. She has primary custody of the two elementary school aged kids. My niece went to her house the other evening. She heard the kids playing inside but no one answered the door. After a long while of loud knocking, the mom finally answered the door. She had been sleeping. Sleeping in early evening while the young children were left unsupervised. Should I bring this up to the non-custodial father?