Need ideas on lighting options as well please! Thanks!

Embrace the yellow...

Considering your walls seem to be white:

- Paint the cabinet the same yellow as your sinks

- Replace the knobs, faucets, towel ring, etc., with matte black

- Replace the mirror and medicine cabinets with ones that have a slim black frame

- Install natural fibre roman shades

- Install a nice printed shower curtain (one show is yellow-white-black)

- Place a flat weave bathroom mat in black & white as well as a hand towel

Edit:

Just saw you want suggestions for lighting, I was under the impression the lighting was under that box above the windows. Please indicate where the lighting can be located.

Yes the lighting is in the box above the windows. But I was thinking about taking that out and replacing with different lightning

It’s also a kids bathroom so I’m thinking of maintaining a kid friendly vibe in there

It's an odd wall to place lighting. If you're able to replace the existing lighting in the box with fixtures that will give good light, perhaps the lighting would be more even along the wall above the vanity.

Since it's a kids bathroom (don't know the sex nor age), I replace the shower curtain with a lively print and a navy & white flat weave bathroom mat.

Lose the curtains ASAP. a roman fold window treatment either fabric or wood fiber

Wallpaper would add lots of personality and then leave the cabinet color as is.

"

- Replace the knobs, faucets, towel ring, etc., with matte black

- Replace the mirror and medicine cabinets with ones that have a slim black frame" indeed

What do you think about using a beachy kid vibe and utilizing colors like oranges yellows blues? Would that go?

Never considered matte black but maybe that would work.
What about the lighting?

What about something like this for lighting?

The large size is 51"

https://www.lumens.com/avanti-led-vanity-light-by-afx-lighting-AFXP454920.html?cgid=21#prefn1=Width&prefv1=Over%2048%20inches&prefn2=tradeOnly&prefv2=No&srule=price-low-to-high-retail&start=0&sz=24&tileIndex=2

Do you need window treatments? The windows are pretty high, and those curtains don't look like they get open and closed.

What about a large stripe wallpaper?

https://www.yorkwallcoverings.com/collections/wallpaper/products/ywd-e30-awning-stripe-wallpaper?variant=40119611785369

https://www.yorkwallcoverings.com/products/ywd-d37-disney-and-pixar-toy-story-4-owens-stripe-wallpaper?variant=39941460230297

I think a either one long tracklight above the windows where the box was or 2 smaller ones would be a better option.

I would forget any window treatments. It's a lot of fussing for what? Try the privacy film that lets light through. So much easier and no dust catchers. I would sooo easy embrace the yellow you have. LVOE yellow. Don't paint the cabinetry. White is perfect for a small bathroom. Where is the light now? In the cornice? I would remove that. Move the electricity to the ceiling. Not a tough job but a messy one. It appears you have the head room for some hanging pendants.

Yes we have lots of room for hanging lights.
The windows already have privacy film on them.
So just no windows treatments at all?

Window treatment gives a finishing touch to any room...

If this were my bathroom and used by kids and I didn't want to do any major upgrades I would do this:

Paint walls and trim a creamy white, Paint the cabinet a darkish turquoise blue, use the same color with a framed oval mirror and do simple blinds for the windows with the same color.

It looks like the vanity top is old fashioned Formica with the square edges. The great thing about this is you don't need to replace the counter. For $100 you can get a sheet of Formica and in a weekend you can cover the Formica with a new sheet. (My niece did this in her kitchen over a weekend as a single mom with little DIY experience.).

Same changes without lightening the counter.

If I absolutely could not change the counter I would do gray greens instead of the turquoise.