She tells us about life with her two girls, why she didn't enjoy her pregnancy and how she found giving birth over 40...
What's Marnie up to at six months?
She's teething - and dribbling! She is very smiley, but not sleeping through the night yet. On average I get about four hours sleep. But I am the queen of the nap. I think it's a parent trait!
There are three years between the girls, did you plan to have that gap?
Not at all. Neither of the girls were planned, life just worked out that way. I know some people who plan babies around things like the school year, but that wasn't the case with us at all. We weren't 'trying' for either of our daughters. Although the girls do get on so well, and I think it's because Florence is old enough to understand who Marnie is, and can appreciate her.
You were pregnant with Marnie at 41. Did you have any anxieties about becoming a mum again over 40?
Not really. I suppose 40 is considered 'old' to be a mum again, but I certainly don't feel like an older mum. You're as young as you feel and I feel great. I know parents who had babies much older than 40. It hasn't been a problem for us at all.
So two gorgeous girls, would you like a third, perhaps a boy?
I don't think so. My family feels very complete with Tom and our two girls. Before I was pregnant with Florence I always thought I would have boys. I have all brothers, and didn't know what little girls were really like as I didn't have sisters growing up. But they are wonderful.
What's Florence into?
She is just learning to read, which is fascinating to watch and listen to. She reads to Marine, which is so sweet, and it's incredible to hear her finding the right sounds and recognising words. Her favourites at the moment are the Mrs Large books - a series about a family of elephants - by Jill Murphy.
That's why I'm supporting the Munch Bunch story writing competition, which asks parents to get creative and submit stories with the help of their children. It's a wonderful idea to help families have fun together.
How did you find both your pregnancies?
I'll be honest, I wasn't a massive fan of being pregnant.
I think parents forget pregnancy very quickly - which is why they have more children!
I felt very ungraceful when I was expecting. It wasn't so much my shape changing and growing, just that I wasn't very agile and couldn't move around as quickly and easily as I normally could, which was frustrating.
You're currently performing in theatre, how do you juggle that with the girls?
It's tough, and I don't have any time for myself, but it's a good type of busy as I love my work. I think anyone juggling a career and childcare has to be flexible. As an actress I am used to that with my work, but it can be tricky. I have help at home, and my mum is a great support. Recently Tom has been away with work for five weeks. That has been tough to manage, but we're getting through it.
Did you feel pressure to lose the baby weight being in the public eye?
You can put as much pressure on yourself as you want - no one else matters.
I'm a great believer in nine months on, nine months off. It doesn't happen overnight. I'm not back to my pre-baby weight, but then Marnie is only six months old...
You've been with Tom for eight years. How did your relationship change when you became parents?
The main thing is we have less time together and on our own, but our girls make our family complete, and we are so close as a unit. Tom has a daughter Nora, seven, from a previous relationship and she is fantastic. Florence adores her and really looks up to her as she is that little bit older.
What's your favourite thing about being a mum?
Waking up in the morning and being covered in kisses and cuddles. The hardest? Spending time away. I love my work, but being apart is tough.
Tamzin Outhwaite is encouraging parents to get creative with their children and enter the Munch Time story writing competition. For more information visit Munchtime.co.uk