Warning-- long, venty ramble likely.
I have 2 sons, 12 and 4.5. Ds12 was my only for almost 8 years! He has always been very attached to me, all the more so because his father has not been very involved in parenting.
He's a very good big brother to ds4.5 (and to the littles that I take care of). Because we homeschool, and I do inhome childcare, ds12 spends a lot of time being the only big kid in a crowd of little ones. This is a role that he enjoys and is good at.
He's also shy and somewhat awkward with peers (not because of lack of exposure, believe me!), and sometimes retreats into the comfortable role of "big brother," or "babysitter's assistant."
Ds12 and I are very close. I do NOT try to place him in the role of an adult-- especially not in parent or partner roles. But, because his father (stbx) has been so chronically absent (emotionally, and often physically) from our family's daily life, ds12 has taken some of the "dad" role, by default.
For example, ds12 is likely to be the one to remind ds4.5 to use the potty before we go out, to play with him while I shower (even if stbx is home) or to give him a piggyback on a long walk (because stbx just isn't there).
Harmless, and reasonable for a much older sibling, yes?
Now I am searching for a job, and preparing for divorce. I want to be especially careful to NOT do what stbx's mom did to him and his brother when she and their dad divorced.
She cast stbx's (older) brother in the "man of the house" role, and stbx in the "child" role (they were 13 and 11). She leaned on the older brother for support and help like he was her husband, and allowed (even encouraged) him to discipline stbx! She worked both boys like servants, but stbx's contributions and opinions didn't count, because he was the "child."
Sadly, stbx is STILL playing the child role-- and this is the root of why we are getting divorced. He acts like a sulky teenager, and immediately "rebels" against ME if I expect him to act like a grown man. He (and his therapist) agree that he is emotionally stuck in early adolescence, and that he reacts to me
as his mother figure by "disobeying" me. :Puke
Stbx's older bro is a great guy, but he certainly has issues, too. He and stbx easily fall into acting like he's the dad and stbx is the kid, even though they're both hitting middle age!
Big bro is as compulsive a go-getter and organizer as stbx is a compulsive thorn in the side of authority (Me.
If you've made it this far, I ask you: how do you avoid letting your older (or younger) kids fall into roles?