Ok shattered it is hard and recognising that and being kind to yourself and treating yourself as you would a friend in the same situation will help.
these are things that helped me; -
Go out every single day, even if it is just to the shops to get milk - the fresh air will lift all your moods and you're less likely to want to kill them if you're outside!
Really work on getting a bedtime routine going - if you know that, eg, come 8 o'clock all will be quiet and you can have some time to yourself then everything will become more bearable . At least once a week make sure that you have a really early night - or if you can't sleep go to bed with a magazine or book so at least you are resting. Everything seems so much worse if you are tired.
Accept all offers of help, even if you find it hard. Make contacts with mums at the school so they can help with the odd school run/ dropping one of them back after a party etc
Seek out other single mums for support - lovely though my married friends are they just don't understand the sheer grind that being a lone parent can be
Get big baskets for their toys and train them to chuck their toys in them - less housework for you.
try to keep at least one room in the house reasonably tidy which is good for your morale if nothing else.
if you find yourself thinking negative thoughts consciously concentrate on things that you are proud of - that you are out of a negative relationship, that your children are lovely, etc.
Treat yourself to something nice once a week - a coffee and a paper in a cafe when they are at school, a new lipstick , a bunch of flowers. It doesn't have to be expensive, just something for you to congratulate yourself on being a mum who is doing the best for her kids.
I hope I don't sound patronising and I know I haven't really dealt with what to do with their energy levels but I honestly think it is more about caring for you so that you have the strength and energy to cope with them.
Good luck - I felt like you two years ago and still sometimes get overwhelmed with it all but my home is so much happier and stable now that I am out of a bad relationship with my dcs' father and the dcs are happier and more stable for it.