You've asked an impossibly broad question. Where are you located? What do you want out of your garden? Do you have children? Do they need play space? Do you enjoy gardening? Do you have time to look after it?

I live in Ontario Canada

Yes have 2 kids and want to keep a good chunk of grass.

I want something low maintenance

I want to have something simple that works with the space

Kids could add a few annuals to it every year but for most part want it to be easy to maintain

My suggestions are about general arrangement, not specific plants. Use what can make the forms and that suits your climate.

I'd start by creating a bed where all the plants are separated out of the lawn. At the beginning, just kill the grass in the bed and mulch it. Add the two trees. And then, add the other plants over time as it suits your schedule and budget. Meanwhile, it will be easy to keep weeds out of the mulch-only area.

Don't let trees keep their lower limbs that are low enough to knock you in the head. Those should be removed before they become too large.