I can kind of understand not feeling so great about your body after having kids. I was a really slim U.K. size 8 when I got married U.S. size 4 and went up 2 sizes after my 3 kids were born. I hadn't got many stretch marks but my boobs were saggy and my tummy bigger and I still think I look horrible with no clothes on.
Sadly my H a few weeks after S no3 was born looked at me (with my clothes on) and told me how huge my stomache was and I really should lose the weight. Now I was able to fit into some of my clothes and thought I looked not too bad but this really made me feel fat and ugly. I really thought well he obviously won't want to ML to me and withdrew emotionally from him.
My H has never seen me in daylight with no clothes on since that day.
Now you seem like a really caring guy and I don't know why your wife can't see that you still think she's gorgeous. If you've never said anything hurtful to her about her weight or body (even teasingly can really hurt).
Although I felt unattractive to my H I would still have wanted to ML and wouldn't have had a problem with him touching me just not with the lights on.
Lots of women HATE their bodies after having kids. Proving that in your eyes she is and always will be beautiful hopefully while not easy will be possible.
Don't have any advice on how to go about this. You seem to be saying and doing some really nice things. I still think you should tell her how bad it feels for you when you are rejected. Once she realises how it makes you feel and how much you desire her sexually it may help her realise that in your eyes she is still beautiful.
I know I bought myself some beautiful silk cami knickers and top that makes me feel I look sexy and hide what I see as my droopy bits. Hopefully others will have better advice on how to progress with this.
