I sometimes feel silly leaving a response on these type of questions, in my 40's, never married and no kids, but I've spent a LOT of time talking with friends about such issues, so I'm diving in anyway! LOL

You mention 50/50 sharing of duties and that is tremendous on your part .... many aren't anywhere near that in helping their mates, but with the age of your children, they are her really BIG responsibility ... and kids that age ... are almost always close to or attached to their mom at a physical level ... in other words ... she already has 2 little people touching her 80% of her waking hours .. and she loves them and adores most of that, but after all that touching, she may not want one more person wanting to touch her in the remaining 20% of her waking time.

If this is the case, maybe making a point of having a couple of nights a week when you take care of all activities with the kids, and one day each weekend get the kids out of the house in an activity ... she can come too, but make sure that the kids are getting time to crawl all over you for most of the time, maybe to the park and let her sit on a bench and read a novel while you take the kids a little farther away. ....

Next, find out (subtly or not) a list of 10 or so things that make her happy .... things that you can do for her, get for her, free up time so she can do, etc. and try to make sure she gets to do at least 1-2 of those things each week .... even if it means pushing her hard to do so. As one of our other pixie-ites mentioned, once she has had some me time on a regular basis, she'll feel the urge to start adding in some us time as well I think!!!

But also know that birth control in any form affects hormones and hormones affect desire for sexual and sensual time, so have her speak with her Dr. about that as well.