Pinkbunny, I have never been lucky enough to have kids. But your children are incredibly lucky to have a mum so dedicated to them.
I know from friends how difficult it is looking after a healthy six month year old never mind one who requires a special level of care.
How about one night in between feeds/hugs etc you set aside some time for yourself. Treat yourself to a nice bath with a glass of wine and then put a soppy DVD on and have some "me" time (since I imagine you rarely sit down). Sod the housework, let it wait.
And while you are soaking in that bath, just congratulate yourself that your children will grow up knowing that they are loved and cared for by their devoted mum.