Hello Tacey,
First of all, please don't be too harsh on yourself. Depression is a very tough illness so in the same way as you wouldn't blame someone with a broken leg for not running a marathon, not being super mum when you are depressed is totally normal. We are all humans and you can't expect perfection at all time! The fact that you are aware that your parenting style has been different is in itself, evidence that you are a great mum!
As a teacher, what I would say to you though is, even though your children are young, they will know something is up and this may cause them a lot of anxiety as they may believe they are responsible for your anger and sadness etc. So, what I would say is, have a nice quiet moment with them and explain that at the moment mummy is feeling a little bit unwell and that's why she is loosing her temper and being sad sometimes. Tell them it's not their fault as mummy loves them very much and they haven't done anything wrong. Just mummy needs time to heal and while she is getting better she may get more angry than usual but this will pass. Children always understand a lot more than we think and once the situation is made clear to them, they'll feel better for it. They made even behave better for you.
I am sending you a big hug, keep fighting, depression does get a lot better with time xxx