I think the trenches change!! The really exhausting part of sleepless nights, constant supervision, never going for a wee alone - you're getting to the end for sure. However, as things change the problems/worries change too. There's nothing worse than a school aged child begging you not to take them to school, or dealing with bullying, or if they are the bully, or if they have something like dyslexia/dyspraxia/adhd/autism and need support/diagnosis/getting school on board etc. It's also then really tricky and hard work worrying about a teenager going out on their own for the first time, or having a bf/gf for the first time, being hormonal and horrid to you sometimes, and gcses and A levels really matter for the rest of their lives in a way that whether you do baby-led weaning, and choosing when to potty train, really doesn't. Plus you can't just pick up a 15 year old and make them listen to you, or carry them home kicking and shouting.
So, I think by aged 3 or 4 ish the whole "oh my God I have to watch them 24/7, live in a soft play centre, never sleep, watch Peppa, deal with tantrums etc" definitely draws to a close (great news you're almost there) but then starts the "will they be OK there without me, will they make friends, what if someone hurts them or is mean, what if they aren't great at school, did we pick the right school, why did mum name her kids Biff, Chip and Kipper and why cant they see that B-A-G is bag not cat" comes next (although i do think the primary years are actually generally ok if things are fairly straightforward) followed by the really big impact full situations like "should they have access to social media, are they having sex, are they smoking, can I smell weed, what if they fail their gcses, how much should we allow alcohol, why are they speaking to me like I'm poo on their shoe etc". I don't think it's ever easy and in some ways, the bigger the child then the bigger the worry. Is it better to be up at night worrying about a party they've gone to and when they're getting home OR because they are 4 months old and need another feed. Not sure tbh. I think ages 4 -6 were pretty good, as school is fairly fun and easy, kids that age aren't that horrible to each other and they're really sweet and chatty, plus easier to control than a bigger child, so I'd choose that age to return to, I think! My mum says she likes parenting a 38 year old - so maybe she's not in any trench now?