As the oldest of 12, I hope my input can be somewhat helpful to you.
My Mom avoided letting us help with the younger children for some years. In fact, I was not ALLOWED to hold a baby or change a diaper until the 7 baby, and only then with Mom or Dad right there working on the 8th baby’s toilet/wardrobe at the same time. In the following years, I was allowed to help more, which I genuinely enjoyed. I was also responsible to be the “built-in babysitter” throughout my junior high and highschool years, as well as when I was home from college. I really didn’t mind this at all, because the little ones and I had good relationships. As you are probably aware, kids typically have more trouble getting along with siblings closer to their own ages, which was true also in my case.
Another thing my Mom did to avoid the stereotype of children taking on too many responsibilities was to delay the delegation of household chores. I wasn’t required to help on a regular basis until I was 7, and then it was only dishes. I REALLY wanted to do the laundry, but my Mom didn’t give that up for another 6 years!!! I could tell why, too… I love doing the laundry!
When the older siblings are reqired to take on parenting roles, their relationships can suffer. It can cause resentment for the elder sibling to be charged with disciplining the younger children. I was not allowed to discipline the children at all, and was often reprimanded just for raising my voice if things got out of hand on my watch. My parents have since relaxed this rule, and now, my sisters in their mid-late teen years are given much more leeway and judgment in dealing with the younger children. I see the problems and the frustration this causes sometimes, and at the same time remember the frustration I went through when I was powerless to do anything.
I guess it is different with every situation, but I would not worry about asking for the help of the older children. I think it gives us a realistic idea of what real life is, when we are expected to do our own parts, and more, when necessary.
I hope this helps, but this is only my subjective experience! God bless you for accepting His blessings so willingly!