I think Flowery gives some good advice, why aren't people like you around when I am recuriting!
It sounds like you have made one clear decision which is your career break for a few years.
Picking up on the HR thread, I have worked in HR for too many years and I love it. It is tough but mentally stimulating and you get to see how organisations work. It is difficult but not impossible to get into, but like Flowery I think choosing your organisation is really important and more so the boss you would report in to. The tough bit is part time.
So my advice is to look into studying / practicing in areas that could help you secure a role.
First you need to get real clarity on whether you really want HR, and if it is what you want then have a clear path to get there.
There are a lot of people I meet in my org who want to get into HR but they tend to want to do what they consider the nice bits of the role and not the tough bits e.g. set up interesting organisational development interventions but not do the employee relations.
What I never understand is that they don't use the HR people in front of them to guide them and advise them.
So I would pick on a HR person you know and take them for coffee, grill them on what they do and how they got there. They may be 'helpful' in articulating how hard it is to get into. Just listen and take what info you need.
Think about whether you could ask to shadow one of them for a day before you go on maternity.
Are there projects you could get involved in for your department/function that work with HR before you go?
Your business must have some sort of employee forum with elected reps, could you do this?
If not look into doing the CIPD and if that is too much to commit to now then see if there are other adult learning courses you could do when your little one is 3+ months e.g. coaching, counselling etc.
If you do the CIPD and need a shoe in to employers but are still off work call up the CAB and see if they need advisers who can search the employment law info and do sessions. Great for your cv.
I have to say whichever areas it is you decide to persue then slowly but steadily just do things that keep you on the path to do it.
Try to do a few things that start to build up for potential interviews.
Last note on your husbands comment. Given that you must have agreed that your career is going to take a back seat for a couple of years his comment is interesting. It clearly made you think, which is never a bad thing. Is he just worried that you'll get bored?