I don't actually have a problem with an MP, or anyone else, having a baby at work in some cases to breastfeed. Of course not all babies may be amenable to this.
I don't think there is anything wrong with this kind of arrangement in many jobs. Not all jobs are the same and we don't need to treat them as if they are. That is just making things difficult for parents for no good reason. Nor do we have to deny women have a physical attachment that is ongoing and different to the attachment men have, that's just a denial of biological reality to prove some abstract point that's false anyway. If a job can be combined with breastfeeding effectively for some mums, great.
That being said, as an MP there would I think that there would be a need for another carer and I am not keen on new babies in creches.
I'm not so sure I think MPs should be on maternity leave, or, for that matter, other types of long term sick leave. It's a unique job in that the public has elected that person, in particular, to represent them for a period of a few years. It's not a job like other jobs. I tend to think that if MPs are going to be unable to do so for a significant amount of time, they should resign and run again at a later time. I would hope that the public would understand that these things sometimes happen unexpectedly and not hold it against them, though I expect some would.
Being an MP isn't a secure position anyone can rely on financially, even always for the election period, so that element isn't a factor in the same way as for most jobs.