Echoing the don't be too hard on yourself. When I first became a SAHM, it took me from breakfast till lunch to make lunch!! It will get easier with practice!!
I try to make food that can be either chopped up and put in one pot to cook, or is super quick and easy. If tea is going to be a while, we do have a snack and it's not always a healthy one. Sometimes we make something (jelly / chocolate crispies) while tea is cooking to encourage good eating!!
I try to get DS to read / practice writing while I cook, he reads to his sister (3 year old supervising 5 year olds homework!!).
We have colouring, playdough and craft stuff, books and toys in the kitchen so they can occupy themselves while I cook too.
There is also a lot of "stop winding your sister up", "can you not do that" and me running out of the kitchen to kiss a bumped knee (and burning the tea in the process!). Sometimes TV works well but I try to keep it till after tea as mine are a bit of a pain to drag away from it once it is on - iplayer works better as it's easier to control when things start and finish, also gets over the "I don't like that one, can I wait till a good one comes on" discussion.
I'm looking forward to better weather when we can go to the park on the way home or play in the garden. Spring / summer is much more fun than winter!!