Its really tough when you have young toddlers who are healthy and active...but kids do adjust and its a case of finding things that you can all do together without you injuring yourself or tiring yourself out. You shouldnt feel guilty that you cant do some of the things other mums do and there are plenty of things you can do with your kids, such as painting, colouring, swimming, cooking, going to an activity centre, museums (they have interactive things for tots), boards games, reading, plant some bulbs in pots, collages etc. There is also nothing wrong with sitting and cuddling and talking to your children either, even toddlers need to take a break at times and this time is an ideal time for you to take the opportunity to rest too.
Some local councils run activities for toddlers such as gym tots etc. Sure start also have quite a few programmes running in areas to get toddlers moving etc. Do your children attend nursery yet? Because if they do then it is likely that they will have lots of games, and physical activities there. There is sometimes useful information on groups/activities etc available through the library or GP surgeries. Meeting up with mums with children the same age as yours and going to a safe park for picnics with a football or something can also be fun for the kids and because they have eachother you can sit on the sidelines shouting encouragement.
If you are really struggling have a chat with your social services, explain that you are disabled or limited in mobilty and that you are having difficulties with some aspects of caring for two young tots. It maybe that they have a group you can all attend or that they can help by providing you with a 'helper' of some kind who can go to places with you and the children and help you to do the things you want to with the children.
Its also a really good time to start explaining to the children why you cant do things and say but we can do this instead...kids do adapt quickly and usually respond positively if they understand what the problem is, even at this age.
As for your ex
!!! Its hard! All I can suggest is that you keep repeating why you are having problems with fatigue, pain and limited mobility. Make sure that he shares the childcare appropriately, giving you much needed time off to rest and to pace yourself. Sort of a chance to re-charge your batteries really.
I'm sure that Little Miss Cheerful wont mind me saying that she is in a similar situation...I will tell her tomorrow!!..and I'm sure she wouldnt mind if you PM her. Hope this helps a little