My experience:
My DS was ND but also adopted so we had a whole other layer of trauma to negotiate. Plus he came to us when he was 3, so when other children were being encouraged to be independent from the parent at nursery and school, he was still learning to trust us and be willing to be dependent, so mixed messages all round, which added to the issues.
School was very tricky, constant phone calls asking me to collect early, or come in for meetings. Wrap round childcare was a complete no-go, far too anxious and needed to know we were there. Ended up homeschooling.
College no better.
Lots of appointments, but also added stuff like self harm and trips to A&E in the middle of the night. Plus a lot of counselling which we had to pay for privately. Some months my salary just about covered the counselling costs.
Now, aged 22, he is working full time but shifts so still needs input to get to work at the right time on the right day, needs help with budgeting, reminding to take meds etc. He gets PIP, so I am basically doing for free what he might pay a PA to do - but he does contribute to the household budget as his monthly income in earnings and PIP are currently over 3 times what I have been earning each month since he joined the family 18 years ago.
I did work but only part time because we wouldn't have coped as a family if I was full time as well. School was soooo stressful, I couldn't have held down a full time job and coped with school and then home schooling.
Breakages are another hidden cost. He wasn't destructive as such, more clumsy and cack-handed, so things got replaced more than might be the case in other households.
He was terribly anxious at bedtimes (trauma from before being with us) so I frequently had to stay with him while he went to sleep which often resulted in me falling asleep early evening, only to be wide awake in the middle of the night (he slept soundly) and then tired in the day, so more likely to fall asleep early evening. Vicious circle.
I would say I am fairly resilient, but there were times I felt totally out of my depth, no support, no understanding from authorities/school. I felt it was my problem to solve and I didn't know how. I started to get panic attacks and not wanting to leave the house.
It still feels like this as I worry what will happen to him when we die, will he be able to cope? Will he have a partner?
He has recently reconnected with his birth family which has added other complications to be negotiated.
It just seems like other people's kids grow up and start to take responsibility for themselves, get married, have their own kids etc, but I am going to be forever parenting him.
Love him to bits, but I feel my life has got lost somewhere along the way.