@Roundhole YANBU. No way in hell would I have been working weekends when mine were little/young/school age, I would never have seen them. I was lucky enough to work 3 days a week in a public services job so I worked Tues, Wed, and Thurs.
I know a number of women who have been SAHM for 10 to 15 years or so, and have (in the last 5 years,) tried to get a part-time job, and literally 9 out of 10 jobs they find, involve shitty hours - incl weekends. Travelodge, Premier Inn, Maccies, Burger King, multiple shops and stores, cafes, restaurants, call centres, all sorts, and NONE of them offer 'normal' 9-5 hours.
In fact, none of them offer anything above an 8-12 hour per week contract, but stick a caveat in, that says 'will work more hours as required,' so they can ask you to do overtime when they're busy.
So you may get 20-30 hours some week, but then they drop your hours back down to 12 for a few weeks, leaving you with less wages. Also leaving you screwed up and messed about if you are on tax credits, universal credit, housing benefit, or council tax benefit etc...
Also many people I know who DO work weekends absolutely HATE it. It does cut into family time/time with the kids. And why the hell should you have to use 'holiday leave' to get weekends off, as someone suggested?
And what makes you so sure your holiday leave request will be accepted? The Manager is within their rights to refuse any specific or particular days/dates if it's inconvenient, or they don't have enough staff that day/weekend.
Pretty bad really. Gone are the days of 9 to 5 hours/school hours, and decent contracts (like a minimum of 24 hours.) Well there are a FEW jobs like this, but they're like gold-dust, and very hard to find (and get.)
Pre mid 1990s, these shitty, low-hour contracts were virtually unheard of. And so was weekend work (for many.) It seems commonplace now, and if you don't like it, you know where the door is!