I'm not HR but I can comment from my experience
The reality for me was , rightly or wrongly that yes two maternity leaves set back my career ,it's only now back on track
However , I realise this will be unpopular but I expected it , for whatever reason at all if you have 6 to 9 to 12 months out of the workforce you have definately got some catching up to do.
I don't entirely agree that it's all about the employer being responsible I worked for third sector and charitable and the reality was that they were impacted by having me off and couldn't leave the post open.
The first one I returned at part time and in time the reality was I struggled at the same grade. A very large part of that was that my Exdh was not helping with child care etc.
I was very established in my career and actually it didn't really help but I do believe it has helped me return to my senior grade in general but bear in mind my DC are 6 and 3
Everyone will have different e experiences, from my point of view I needed current experience to stay at my level but if I had a trade so to speak like a nurse pin number it may have been simpler (although then of course shift work which is a bugger to cover)
My advice would be ,be realistic , I personally think it's irrelevant the views of HR as they don't often make the decision to hire. And if your prospective line manager has an issue you don't want to work for them anyway
With ds2 I accepted my career would stall and that was ok , I always worked but I had to accept promotion wasn't likely to be an option for the first year
So I accepted it and when they got older geared up again (I'm the higher earner in the family so staying at home for me was not an option)
Make sure your DP or DH understands the impact properly and will help ,not doing that killed my marriage and God knows doing a senior management role as a single parent to two under 5 pretty much nearly killed me
Be realistic and accept it but don't try to work for anti family companies if you can help it it's not worth it...the stress would be horrendous
Don't know if any of that helps purely my experience