Hi OP, mother to 2 young children here, thought I'd give you my views as somebody on the opposite end of it,
Me and my partner used be very spicy (is that a suited word lol?) in the bedroom, but as with most couples, it fizzled out to vanilla after having kids.
For all kinds of reasons! - I'm tired, i don't feel sexy, I don't have the time, when I'm up for it, he's asleep, and vice versa and so on.
We spoke about it in depth and a lot of my issues stemmed from being tired, somebody always needs me and something always needs doing - and I get little help from him. I wonder if your partner could be feeling similar?
I told him very openly and honestly that if he helped more, I would have more time for me / us and it would help - and it helped!
We now often joke about it and when he's helping clean up and tidy etc, I often say things to him like 'oh there's nothing sexier than a man that knows his way around a hoover' 🤣
It also took me a long long time to open up and speak to him about things I'd like to try in our sex life. I almost felt embarrassed when first speaking about to it, but I've told him and we now talk about stuff often, a lot of it on my part is said in a humorous way as I am the most awkward person on the planet but we're communicating and it's nice.
I'm pregnant again so the tiredness has gone up, he's being very understanding and supportive etc. another big issue of mine was 'losing' myself after becoming a mother. Not just physically but mentally too, I silently suffered post natal depression for a long time and that added to other issues, I pressured myself into being the 'perfect' mother and partner. And the body changes did not help, probably TMI but since breastfeeding my booobs haven't stopped leaking and I found that so embarrassing, thought my partner would despise me for it but he understands and again, it's become something we both accept and laugh at.
Women tend to be very in touch emotionally too, if I'm not ok emotionally outside of the bedroom, things will not be ok in the bedroom.
I'd suggest talking to her lightly without pressure, don't even focus on the sex part at first! Just make time to find little sparks through everything else together, make her a meal on night and watch her fave film with her, ask her random questions, get to know her deeper as a mother - we change ALOT after having kids and sometimes we don't recognise ourselves. Be patient and be an open book, she loves you, she may just not have much energy. X