I didn't want a big family. Realizing my kids will rely on each other when I'm gone made me have 3.

• Nina Goodwin, 40, wanted a maximum of two kids and never planned to have any in her 40s.

• Then, her first daughter was born with Down syndrome.

• She didn't want her second daughter to be responsible for her sister's care.

This as-told-to essay is based on a conversation with Nina Goodwin. It has been edited for length and clarity.

I never initially planned to have a baby in my 40s.

In fact, as I already had two kids and had never actually wanted a third, it was never something I thought I'd find myself pining for and trying so hard for — even at risk to my own health.

My husband, Will, had wanted a big family. Two was my limit. I remember saying, "I'm the one who's got to carry that child."

Everything changed when I gave birth to my first beautiful daughter, Mabel. We were told she had Down syndrome. I found the shock and grief quite overwhelming.

I was focused on her

Back then, the idea of having three kids was out of the question. All I could think about was, "How am I even going to parent this one child?" The thought of having any more with the risk of them also being neurodivergent was too unbearable to imagine.

Then, I connected with the Down syndrome community and started processing it. I noticed many Down syndrome kids had lots of siblings. I learned how they have more support and love the social aspect of being surrounded by people they trust and who love them.

I wanted Mabel to grow up with a brother or sister who shared a close bond so she wouldn't feel isolated. So, along came Nancy.

I liked that she was another girl; it meant she'd be caring toward Mabel.

My second child helped me a lot

We knew there'd come a time when Nancy's development would overtake her older sister's. That's already happened — Mabel is 7, and Nancy is 5. If I can't get Mabel to do anything, you can guarantee Nancy will do it. She'll dress her. Put her on the toilet. Read to her. Mabel always says, "You be mom, Nancy, you be mom!"

But as I saw this unfolding, I had a darker realization.

If Mabel was already seeing Nancy as a second mom, I saw that play out in the future. I didn't want all the burden of care to fall on Nancy for the rest of her life.

What if something happened to me and Will, and she felt duty-bound to be Mabel's carer forever? Or when we naturally go, and all our kids outlive us? I didn't want Nancy to feel shackled. It made me feel guilty.

Maybe Nancy will happily be the sibling carer. But maybe she wants to be a free spirit and travel the world, doing all the things young people should have the freedom to do. Yet she feels she has to compromise those dreams to care for her sister as her parents age, become more frail, and then die. Nancy never chose that for herself. I was maybe catastrophizing, but the guilt ate me up.

And so along came Edith, who's now 4 months old.

People didn't understand why I wanted a 3rd

It was a traumatic journey to have Edith. At first, some friends didn't understand why I'd have a third when I already found it tough having two kids and a full-time banking job.

I was determined, though. I had three miscarriages before having Edith. Physically and mentally, my body's really been through it, so I haven't come out of this pregnancy in great mental health. I don't feel seven years older than when I first became a mom; I feel 20 years older. It'll get better; I'm just trying to get used to life as a family of five.

The upside is that the crushing guilt I felt lifted the minute Edith arrived, and I relaxed a bit. Of course, Edith may also want to be her own person. But now the responsibility of care for Mabel is shared after I'm no longer here or able. Some of the grief about giving birth to a disabled child — which is taboo to discuss — has also been healed as a result.

I feel terrible using the words "burden" or "responsibility," especially because Mabel may also develop into a very independent person.

As the girls age, my message for them about Mabel will be the same as any mom's message to her kids: Look after each other.

Financially, we've set up a trust for Mabel so she can do what she enjoys. She might want to go to college, or go on holidays, or go to raves.

Ultimately, I want all my daughters to do two things in life: fulfill their potential and be happy. Now I have three — against all odds — I really feel I've done all I can to set them up for that.

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