I am pretty sure IANBU. But I may be biased by wanting the 1.5 days 'off' 
I have a 2.5 y o and a 3 month old. I've been on maternity leave since may. Toddler has obviously been out of nursery during lockdown and returned this month. He goes 1.5 days per week, the minimum allowed by the nursery while I'm on maternity leave (usually goes 3 days).
He is naturally quiet and reserved. He is a creature of habit and thrives on routine. He is also very attached.
He has been at nursery since 10 months old and when lockdown happened, we were just getting to the stage where he did cling/cry at drop off.
MIL is being very disapproving of toddler being kept in nursery while I'm on maternity leave because of the cost.
If we took him out, I'd have to deal with the emotional impact of both being upset going to nursery when I go back to work. He'd be harder to settle again and we'd be back to square one. He hasn't taken well to being dropped off after 4 months off and is very emotional about it again.
We can afford the nursery fees. We generally live fairly frugally (apart from a high mortgage), we still save every month. Okay we don't have pots of money set aside, but we're 30, have two children, a sizeable but perfectly manageable mortgage and we're saving money for long term, overpaying our mortgage and saving for more immediate circumstances - holidays etc. We don't do loads of expensive hobbies for toddler but parks, walks, reading, songs, playing etc rather than the groups/sports classes.
Toddler also enjoys nursery while he's there. He has lots of friends, and as soon as I leave, he's perfectly happily playing after cuddles with his key worker - I call to check.
While toddler is at nursery, baby gets one solo parenting time - in the way that toddler did when he was a baby.
Also I get to just 'be' with baby, drink tea while it's hot, go to the loo on my own and get some houses done.
AIBU? Am I blinkered by the benefits to me?