Difficult one. As for timing of telling you, I imagine that will depend on your employer.
You sound annoyed by this (probably rightly so!) but if it is a mandatory course for your job then there isn't too much you can do about it, and they will probably never run courses like this part-time. If this is going to cause problems with childcare or travel, I would talk to your employer about it but don't go in all guns blazing. Say that you know you need to go on this course but it causes some big difficulties so can you talk to them about this. And of course discuss whether it will be overtime or time off in lieu. It might be that you have to have a horrible 3 days around the course, but then get the rest of the week or more off.
That is a slightly different matter to your op . If you have had leave approved for 2 of the proposed training days then you can't go, if you have requested it presumably they won't approve it. Did the course date change or is there still an alternative in October ?
So how much notice did you actually get? Why can't you go to the training in October as originally planned? I think it depends if it's a genuine error (mix-up with dates) or if they have changed things and just expect you to fall into line.
Are they the same plans that involved taking holiday which has not been approved yet? Or plans that you could still do if you didn't have the holiday approved? Because as the holiday hasn't been approved, the "staying with family" plans weren't firm were they?
Have you actually spoken to your line manager about it? If you explain that you were expecting to go in October, and that it would be difficult for you to attend the earlier date, they may well be happy to stick to the original date, and this will be a non issue.
If not....well, then you could have to make a difficult choice, I suppose.
I work part time and only have childcare booked for the hours I work. Finding childcare outside of these hours is difficult-my plotter knows this and understands that I will need as much notice as possible to work additional days. Sometimes, good communication makes all the difference.
Do you ever have to vary your hours apart from this? Is there anything intrinsic to the role that requires you to be flexible? If no (and given that other staff had a lot more notice) then I think you would be within your rights to say that you couldn't make it.
I work pt and would go in (and have in the past) provided I hadn't made other plans that were important to me. I also expect a bit of give and take- I try to be flexible, but I expect my employers to show me the same courtesy as other members of staff. That means giving me the same notice as others- or more given that it's outside my normal working hours.
Five days notice of training is not reasonable when you only work part-time. Even if you hadn't requested leave for two of those days, presumably you would need time to make childcare arrangements to work three full days when you normally only work 3.5 hours? It sounds as if the training date was changed from October, the people in charge forgot to tell you and it only came to light when you requested leave and they realised there was a clash!
What would happen if you told them you had made arrangements to work the three full days in October and couldn't change them at this kind of notice?