A LOT of primary teachers drop down to part time work when they have children as full time is just too much to also have any family life. But I've also know plenty who have multiple children, work full time and have a wonderful active life with their children outside of work. One woman who immediately springs to mind, I met when she came back to work (I'd recently started at the school) after her third child. She was Maths Lead, so lots of extra responsibility. She would be in by 8 but often left 'early' (i.e) 4.30pm two days a week, 5pm (ish!) after staff meeting and leadership meetings twice per week, and 4pm Fridays. She then often worked after she'd got all 3 kids to bed. Super women, but she was a fabulous teacher and somehow juggled it all. I'd often see on Facebook her family trips out at the weekends. Oh and she was mainly a single mum (odd times she was together with useless partner). Significantly, she had her mum help out a lot, who lived just down the road from her.
A lot in primary school really depends on the school and the ethos of the head teacher. A lot are awful with expectations of work. Pre-children, I'd found a fantastic position. I left home at 7.20 to be in school for 8. I'd usually leave at 6 to get all work done (home by 6.45) but could leave much earlier if needed. And I'd finally got to the point where I wasn't bringing any work home evenings, weekends or holidays unless there was a 'project' on (report writing, implementing something new, etc). However, for me, I didn't want to see nothing of my child during the week. I could have left earlier but that would have meant working after bedtime and weekends. So I left teaching. I probably would have considered part time but moved on to something else.
In teaching, there is ALWAYS something more you could be doing. You kind of have your absolute must do list because your books, planning and classroom environment are going to be monitored by leadership, and then your 'other' list that would have a great impact on the children, but you'll do it if you can catch up with everything else first.
I did really love the job though - but I'd gone through hell at another school with horrific work expectations and bullying (which is sadly very very common). What I always loved about the job was that I had so much autonomy really (I'd guess if you speak to lots of primary teachers they might not think this is true if they are thinking about how often their lessons, planning and books are monitored). I got to work and left in the evening when I wanted (obviously outside the directed time). If I wanted to meet friends at 4pm on Friday, I could. If it snowed and I wanted to scrap all my lessons and do a day basing everything around the snow, I could (not in all schools). My workload was completely my responsibility - no one told me: Mark books now, write an assessment now, do a display now (obviously I had to work within time lines given, and schools will often have policies that displays must be changed each half term, books must be marked in depth x times per week, etc. But the actual organising of my time around those policies was down to me).
One last thing to consider, and I actually hate to bring it up, but think it does need to be considered. But anything you do decide to do, you really need to be certain you could afford child care for it without your mum's help. Non of us ever really know what is around the corner, and a sudden long term illness, for example, could mean that she is no longer able to provide that for you.
Good luck in whatever you do decide (and I did a complete career change at 36, and now my husband is doing one at 38.)