it takes two to make a quarrel
Two parties involved in a disagreement, argument, or fight are usually both responsible in some way (as opposed to it being the fault or responsibility of one alone). Your son blames mine for their fight at school, but it generally takes two to make a quarrel.
It takes two to make a quarrel.
Prov. An argument is never only one person's fault.; If the other person refuses to participate, there cannot be an argument. Sue: I think Mimi ought to apologize for arguing with me. Mother: It takes two to make a quarrel, dear. Maybe you ought to apologize to her. Jill: Why are you always so quarrelsome? Jane: Hey, it's not just my fault. It takes two to make a quarrel.