Explaining death to young children

I don’t even know where to start. My mom lost her battle to mental illness yesterday. She was very involved in my kids’ lives (4 years old and 18 months.) It has been very traumatic to say the least. My husband and I are so worried about our 4 year old and how to tell her. Is attending the viewing/funeral necessary at this age? She was close with my mom, but we’ve never experienced a death like this in the family. We are so worried about traumatizing her and how to explain it to her in a way that won’t scare her. Would it be wrong to keep her and my 18 month home from the funeral/viewing? I know there’s no right or wrong way to grieve, but I’m so worried about my kids and their well being. I’m just looking to see if anyone has any advice or insight. Thanks all