‘Tell me, what is it you plan to do with your one wild and precious life?’

Have you read the whole poem that quote comes from? Not to diminish your ambitions, but it's not about doing epic things at all, quite the opposite:

The summer day by Mary J Oliver - Famous poems, famous poets. - All Poetry

I read it that the op wanted to do something that her grown up son would be proud of her, not the toddler he currently is.

@Sadalot90 I don't really have a suggestion, but I have been impressed by friends and relatives who have retrained in a profession, mainly into teaching after being a TA for a while, or even in a completely different profession in the case of my cousin.
I would just say do something you want to do.

Stand for elected office?

I'm hoping to get a project off the ground that will make a big difference to the lives of some very vulnerable women. There are a lot of challenges to overcome. It won't be 'epic' as its small scale, but it matters and gives me a sense of purpose.

It's very hard to do "epic" things when your dc are so young and need you so much. Everything costs time and money.

I agree with the above poster that your dc won't care, do something for yourself.

Maybe I'm too boring and practical, but I'd say investing time and effort in your career is probably the thing that's going to most benefit your dc.

I would ask what you value in life - is it the work done by charities or voluntary groups? If so, you could volunteer or fundraise.

Is it challenging yourself to beat your own limits? Plenty of physical challenges to attempt. Which you could also do for charity.

Is it to improve your education and career? I know many mums who have gained professional or educational qualifications - a great achievement.

I think you need to think about who you are and what you want- good luck!

I wouldn’t be trying to impress a toddler. I write novels for a living and people are always saying on Mn that publishing a novel is one of their dreams and a generally impressive and inspirational thing to do, but my DS thinks it’s the dullest possible job and basically involves typing. 😀

One of my friends does extreme ultramarathons and has done seven marathons in seven days on seven continents, and his children think he should get a life and do fun stuff.

Do what you want to do, OP.

Unless you start shitting toys, I doubt your toddler will care at all! So if you want to do something epic, it needs to be something YOU want to do. Even when they are older, you might find they are underwhelmed with your achievements. Maybe as adults they will appreciate...
I guess you probably want to think of what is possible. Some things might take more time and/or preparation than you have. Eg, if you want to run a marathon, you are going to have to spend a lot of time training. If you want to walk the Inca Trail, it is going to take a lot of money and time away.
You could do a skydive?
Or maybe do something more inspirational like commit to volunteering at a community project or something.