Child seems to take joy in another child being punished

A little background: I have a 4.5 year old that has mostly nonverbal autism. She communicates in other ways (mostly signing). I've been babysitting for 3 other children who are all (as far as we know) neurotypical. They are a 7 year old boy, a 5 year old boy, and a 1.5 year old girl. They are at my house Monday - Friday.The boys are generally well behaved and don't have many issues other than typical child attitude and misbehaviors. The little girl is a tornado and my daughter is the same way. This leads to me having to discipline them more than the boys which is kind of expected with the age difference and the neuro differences.My problem comes from the fact that over the last week or so the 5 year old seems to genuinely take joy out of the moments when I have to discipline my daughter and his attitude gets visibly worse when I have to discipline his sister. He will have a devilish smirk on his face when I give my daughter a time out and give me dirty looks when I have to do the same for his sister. Does anyone know why this may be or if there is any way for me to deter the behavior? I'm worried that it could potentially escalate to him trying to get my daughter in trouble on purpose.Edit to add: I've talked to the mom and I don't discipline any way different than how she does and she has been present when I've disciplined them before so she is aware of how everything runs in my home. via /r/Parenting https://ift.tt/2M5o3tY