I have 6 and they are certainly not 'processed'.
Do I have days where life is frazzled and it feels like all I've done is feed them and keep them alive - yes. I also had those days when I had 2, and I don't have them any more frequently than I do with 6.
We're fortunate enough that when we got to the stage of time starting to be an issue I could give up work (initially for a few years, now long term as other circumstances have changed) which made life easier and meant that I didn't feel they were missing out on time.
We're also very lucky in that my MIL and my other MIL (DH was a widow with DS1 when I met him) absolutely dote on all of the kids. So this weekend coming for example I'm taking my two eldest girls to a festival, the middle two are going to Legoland with MIL and my youngest (who has significant health issues) is going to somewhere she loves with OMIL. Eldest is going to the festival with his friends and if we see him I've not to fuss or ask if he's ok. They get more decent one-on-one time than the girls did when I was a single parent, working full time and juggling everything.
Do I regret having a big family - no.
However (and as someone who was unwanted andabused as a child DD4 will never ever know this) I do regret the situation with my youngest child. I fell pregnant on the coil. Had a difficult pregnancy (I went for a termination and requested not to show the scan screen, but a the staff member decided to turn it round and show me 'the healthy wee heartbeat' and I couldn't do it) and then her birth was disasterous. The damage and health issues she have been left with have a huge impact on us and it takes everything DH and I have to make sure the quality of life the other children have hasnt suffered long term.
I'm angry that I was told I was too young to be sterilised in my mid 30's with 5 kids. I'm angry that the sonographer - knowing my wishes - decided to ignore them. I'm also angry that the man whose lack of care during her birth damaged my DD apologised and got on with his life whereas she and the rest of us will have to live with the consequences forever. Counselling has been a godsend with that an I'm now much less angry than I was.
My older kids don't look after the younger ones. It's funny that people assume they do though. People often ask them to babysit assuming they have a lot of experience of being hands on with young children. One of my DD's (16yo) has always loved babies an children so has a thriving babysitting business on the go. I couldn't afford her rates!!
I will admit we had a six month spell where it was all hands on deck when DS1 was 16 and DDs were 14 when DH had the chance to work abroad for six months. That was the only time they ever had to pitch in more, but that was more that for those six months there were less lifts, they had a few more house chores rather than being hands on with the younger three (we hired an au pair to help with the younger kids and my PIL were wonderful). It was a crazy time, but that period set us all up for life basically. It funded extending our house to give more space , we'll have money to help properly through uni (especially if/when the twins go at the same time) and DH was able to change his job after to one that gives him an 8-4 day, which in turn helps with the one-to-one time as well as holidays and just having a financial security that we never expected to have.