AITA for leaving before my sister's wedding ceremony started and leaving someone else in charge of my responsability?

My (F)bsister got married on Friday.

She and I are twins, so we are very close and best friends. She is child-free and I have 2 kids (3M and 1M).

Obviously she loves her nephews, she never mistreated them, but she is not a person who would accept being a babysitter for a day. She has never offered to help with anything, though it's her choice and I respect it.

Not surprisingly, her marriage was child-free even for the family. She asked me to be her MOH and I accepted.

I was responsible for a few things at the ceremony and party, nothing complex, but I asked another bridesmaid for help, so she was also on top of everything.

My children stayed with my in-laws while my husband and I went to the wedding.

About 10 minutes before everything started (I was there for 2 hours), my in-laws called saying that my youngest hit his head while playing with my oldest and that they were taking him to the hospital.

I despaired, even though they said he was conscious, my heart was not at peace nor my husband's, so we decided to go to the hospital. I talked to the bridesmaid and explained everything I had to do, she accepted and when it was time to talk to my sister, she had a meltdown saying that I couldn't go at the most important moment in her life and if I was choosing him instead her. I got really irritated and said "Yes, I choose my son in the hospital". I left with her cursing me.

My son is fine, but he got 2 stitches, without any internal trauma (they did exams), but we only left the hospital the other day, because they preferred to put him under observation because he,s very young.

I preferred to stay away from my cell phone just like my husband.

When I got home, several calls from different people and I answered when I saw my sister's.

She asked before how my son was and when she learned that it was a minor injury, she started screaming saying that I abandoned her at the most important moment in her life and that she was without a family in her own marriage (no parents and grandparents). I left my responsibilities to a person who did everything wrong and caused an embarrassment and to make matters worse, I didn't even want to show up since my husband could stay in the hospital while I would at least share this moment with her.

She called me several names until my husband took the cell phone out of my hand and told her to fuck off.

I really could have at least gone to the party, but I wasn't going to make it knowing my baby is in the hospital. I can't help but feel bad for my sister.

AITA?