Hi Shonna
I think with girls it's a bit easier, because we have that mother instinct right from the start of our lives.
When my stomach started showing, I started explaining to Nienke what is in my stomach. We spoke about her brother a LOT. I bought her a baby boy doll and we played with him. In the bath, I'd let her stroke my stomach, she put her ear to my stomach, I told her her brother is saying he loves her and he cannot wait to meet her. I explained that when he is born, he will not be able to play, since he first has to grow. He is small and will cry, poo and sleep.

She seemed to be okay with this. We looked at tonnes of scan pictures, we'd read baby books together. She sometimes wanted to see how the baby grows and then I'd take a book and we'd go through it together.
My mission was not so cope with baby and toddler but to help form a bond between my two kids. I didn't want her to feel excluded or as if she matters less. I told her a lot that she might feel she is getting less attention but its only because a little baby cannot do anything for himself.
When I went to hospital, she was still asleep and her nanny came in. The nanny told her that I went to hospital to see if her baby brother was ready to come out of my stomach. I later phoned her and told her about her brother. I was very emotional (read hysterically crying) the whole day of his birth because the pead refused to send us home immediately (long story), so I didn't want her to see me like that. She came the next morning. When we saw each other, we burst into tears!
She asked to hold him and immediately he was "her" baby. She held him so much those first few weeks. I let her stroke him and lie with me when I breastfed and talk to him. We tried to include her with everything. The first few days, if he cried, she'd be hysterical, because she felt he was unhappy. She also started waking up if he moved during the night (she was in our room at this stage). But after a week or two, she went back to sleeping through and she was okay with him crying.
I am so lucky that there hasn't even been one day of jealousy from her side. She really, really loves her brother so much. In the beginning, you could see her voice was too loud for him. He'd get irritated. She was in his face all the time. But he realized he'd have to get used to it and now he LOVES her. When he sees her he smiles and starts kicking like crazy.