Being pushed to go full time from 4 days

[Noneofmybeeswax]

I work in a team of 4 and our boss recently got sacked. We are overstretched anyway so while a new manager is recruited in I offered to up my days to FT to help. I thought I was being clever and showing that I'm a keen, team player who wants to help the business at a difficult time.
Yesterday my senior manager announced that he'd like to take me up on my offer and he'd get my new contract sent out. When I quizzed him it seems he has decided that this should be a permanent move. I don't want to do that. It will be a childcare issue in school holidays (I can manage easter and we're away in half term anyway) but summer will be a nightmare and I enjoy my time with my young primary age kids. The extra money would be lovely but I highly value my 6 hours a week to get all my chores done.
Is Senior manager being a CF and I can tell him to bog off or have I backed myself into a corner I can't get out of without looking like I don't care?

Were you clear it was only a short term offer?

Just remind him the offer was to be temporary to help out. Put a time limit on it

I was quite clear that it was to help out for a while and his only concession was that we could write it into the contract that I could have a review but i suspect that would take the form of a new flexible working request and that would be easy for them to reject given the circumstances.

I'd just rescind the offer.

Senior manager isn't a cf. Doesn't seem clear that you meant it as temporary. I'd have called it over time not increasing hours

Anyway you could tell him your Childcare issue and counter offer to do 5 days in term time only? Showing willing and solving your Childcare issue in the holidays at the same time. Nither of you sound like CF, just sounds like a miscommunication