Try to talk and listen - put the sex aspect aside as she has said she feels busy, things on her mind, sounds like she can't relax and 'feel' sexual
If you can have a talk together and approach it with her in mind to begin with and put your feelings about sex/affection to one side, and really listen and try to see if her stresses can be helped at all
So she's busy and has things on her mind - is it the house/children making her busy and feel like she can't switch off? Can you look at and consider together that you have enough childcare? Is it worth having one day where the children are looked after and she isnt working where she can make sure she has a bath in pease/reads a book/watches trash tv for a bit, has some time to reset and recharge? Parenting all day can make it really hard to switch off from being 'mum' and becoming a partner/wife again. Children can also make you really 'touched out' where you are being hugged/pulled/whatever else all day and can't stop those interactions as it's part of parenting. But then just need your body and space when it finally stops
If finances allow then household help like a cleaner might help (again depends if you can begin talking/connecting and if the household is causing stressed)
If they're at school and she already has that then just a talk about if she is feeling stressed - trying to work out the reasons and route cause between her feeling busy and like she has a lot on her mind
The one thing you don't want to do if she has a lot of demands and pressures in daily life from organising children/home/appointments etc is to make it feel like sex is something else she needs to tick off the list. Which is why I say to just not raise it and put it to one side for a bit to see if you can find the route cause. I do understand it will feel like rejection her not wanting it etc, but if her head is full of other noise and chores/things for the children, then adding the stress of your needs will feel worse to her as opposed to better.
Hopefully if you can talk and connect and become a team in life things might just begin to improve