Do you ask older siblings to watch younger siblings?

My boyfriend has 5 kids from his first marriage, the 11 year old boy stays with us, and the 9 year old girl and 4 year old girl are here part time. The 9 year old always helps me with the baby, she will be watching tv and I’ll set my son up on the floor with a few toys he’s 9 months btw and she will keep and eye on him while I get dishes done for something. Honesty the 4 year old will watch him if I have to go to bathroom or something. She knows to take things from him that aren’t toys and yell if he’s getting into things so I can pee faster. Today I went to lay down with with my son for a nap and as soon and we laid down and my son woke up and I’m like exhausted and I gotta be at work in an hour so I really only have 30 minutes to nap. So I was like fuck it I put my son down in his walker and put the walker down in the 11 year olds room. I tried to talk to the 11 year old but he has his headphones in and is on his stupid video games and couldn’t hear me and literally its like 20 minutes I didn’t even really needed him to watch him just didn’t want my son running around the whole house in his walker. And not even 10 minutes later the 11 year old comes in my room, wakes me and gives me the baby. Like I know I didn’t talk to him but still I have my door closed I have the light off, like you can’t just let the baby run around your room for 10 minutes.

Do you guys have older siblings help with younger siblings?