Am I unreasonable not to agree to his new child access rota

@Aiming4Optimistic I see that. All good reasons as to why becoming a ft SAHP is not a sensible idea.
It also makes it harder to get back into work (which OP will need to do) in order to financially support her children if significant gaps in employment history.
At what age is childcare funded now? I think it's changed relatively recently (my youngest is 6).

Sometimes a mum has been put at a financial disadvantage by sah with young children, or by facilitating a partner who works away and hasn't been around to do their fair share. It's often difficult to go back to work when there are huge chunks of time where the dad isn't available to to his bit. OP has full responsibility for the dc for weeks at a time where there is zero help available from dad and that probably has an impact on her ability to work. Plus she has a 2 year old.

If mum was suddenly as unavailable as dad, who would look after the kids?

So while she has to continue putting his job first to a large degree because it's financially necessary, there has to be acknowledgement that ex can only maintain this work pattern because OP is picking up his slack, when it comes to childcare.
Although they are divorced, there's no such thing as complete separation when you have dependent children and financial commitments. Ex needs her as much as she needs him, for the time being.

I would encourage OP to get back into work when she can because it's better for her if she doesn't need anything from her ex but possibly it's just too hard to do right now. We don't know where she lives and availability of good childcare, what she's qualified to do, travel situation or availability of appropriate work.

@MeetMeOnTheCorner Why "most men" but not "most women"?
Once separated I don't think it is reasonable for father to work to provide everything financially whilst mother does not, meaning that she has more time with their children
There should be a more equal status quo.
My children lived 50/50 between myself and ex-husband for a good number of years and absolutely we both worked in order to be present parents and provide financially for them.

@Cheeseandolivesplease He’s not penalized! He’s just around less! Most men accept working means less time to see dc and sometimes this applies to the mum. It’s time available that matters and stability for dc that meets their needs. Many parents are not in a position to pick and choose work hours! Life is not like that.

@Blondeshavemorefun So does Father.
Father, in this instance, clearly wants to have regular contact with his children just as mum does.
So why should he be "penalised" for working by seeing his kids less?
Being a single parent does not mean you can't work. In fact; it means you need to step up and take financial responsibility for your children along with the other biological parent.
Ask me how I know.

She has a 2yr

You asked why she's not in work. She's already said she's not in work so she's fine to change care arrangements. Why do you need to know why she's not in work?

@RoseField1 Of course it is in terms of a reasonable child arrangements order.
For example, Father should not be told he can only have the kids certain times 'as he is working to provide' but yet Mother argues she can have them more as she is not? That sort of thing.

Why are you asking that? Is it relevant?

@CoverLikelyZebra It’s important the older child has a voice in this too. Any changes should not be disruptive to the older child in terms of school and hobbies. Just saying what adults want does not take into account the needs of either child.

The existing arrangement is very typical for a court ordered arrangement. It’s essentially 9 out of 15 nights to dad when he’s not working. Many child arrangements are 9/15 nights to mum 52 weeks of the year or holiday arrangements clearly defined. In this case, the dad cannot do 52 weeks, so he gets more time when he can have them. That’s seems ok to me. That pattern could be continued for the 3 week or 22 night rota. I just would check it works for dc. It means op has dc for much more because dad probably cannot have dc for 2 or 3 weeks at a time and the court recognised this.

He doesn’t seem a bad dad to me and clearly wants engagement with dc.

Sorry @Princess90x , my intention didn’t come out well.

What I meant was that I agree he isn’t seeing his dcs much.
I agree that 3 weeks wo seeing them is long, esp for the youngest.

But the devil’s advocate would say it would be the same if you were still together iyswim.

May I ask why you are not in work, OP? @Princess90x

Good job that's not what he is seeking!

NO NEED to SHOUT!

you have misread - the child is away from
dad 3 weeks and with mum 100% during that time, suppose you think that’s fine!

STICK TO THE COURT ORDER.. sorry I need to stress that!!
NO TODDLER NEEDS TO BE AWAY FROM THEIR DM FOR 3 WEEKS. I DOUNT A COURT WILL GRANT THAT.

I'm afraid your communication isn't very clear and that might be contributing to the difficulties you are having with your Ex.

If I understand it correctly, the current setup has you being solo parent with nothing from him for the part of his rota where he is working then within his 14 days off work he has a day of "actual rest" then 4 nights solo parenting, then the kids come back to you for 3 nights then he does another 4 nights solo parenting, then he gets another full day off with no childcare and then back to work.
So across 28 days he has them for 8 and you have them for 20, but during his time off work you are doing as much as possible to maximise their time with him whilst also ensuring they don't miss mum too much with very long gaps.

Its annoying that his work schedule is changing so soon after this was agreed but he can't help that it should be possible to agree a similar kind of schedule for a 3 week cycle and you both ought to be sufficiently grown up to take the principles of the court-ordered structure and apply them to the new setup.

What would seem a reasonable pattern to me if I was mediating this would be that within the 21 non working days on the new schedule he should have first a day off, then 4 nights with the kids, then they come back to you for 2 nights, then he has 5 nights again, then back to you for 2 nights, then 4 more nights with him. So across 42 nights you would have them for 29 nights and him for 13 which is a similar percentage slit as it is on the 2-week setup.

If it wouldn't cause other issues it would also be reasonable for him to increase what he does, as capacity allows, and perhaps instead they do 8 nights with him, 3 nights with you, then 8 nights with him in order to get closer to 50:50 care - but only if this is actually in the best interests of the children. Whether to push more for one or the other of these models should be 100% based on what the children will most benefit from, not some misplaced idea of "fairness" between the adults. The children are real people, not ways to score points.

My head hurts. I need a years planning calendar , his rota & a pack of coloured pencils.

Whats your financial agreement?

I think that unless you aren't relying on him at all for child support, then you probably do have to be more flexible. Obv if you were independently wealthy and didn't need his wages at all, you can afford to be less cooperative, but if his job is essential to yours/the dc support then work has to come first.

Im pleased it's not just me & other feel the same!

Well that depends in if he has has any say in his work rota changing.

@Princess90x he's said he's going to go to court, so just leave it with him.

Like a PP I can't work out when he has them
now & when he wants to have them, but if it means he has them on days off rather than work days I'd go with that because it's better for the kids. Plus if necessary, get CMS changed.

I don’t get how it could be 53/47% like says in op

what do you doe for childcare when you work @Princess90x

But there not extra nights, it's the same split but over 3 weeks