Hi Joshua! The image is very sweet. I like the grandma character a lot.
I think the biggest improvement would be better value structure. Just more contrast and better silhoullettes, value consistency within bigger shapes, clear edges will help a lot. Comparing adjacent colors : is it darker/lighter , is it warmer / cooler color?
Maybe just thinking, what time of a day, weather and light condition you want, might help. And get reference for it if needed. To me it feels like there is a wet, foggy weather in the park, which doesnt corespond with the storybeat.
The limited color pallette is a nice idea, but the colors feel a bit incosistent for instance in the girls hair (i suspect you used red to attract more attention).
Some other ideas to try:
Some experimenting with poses (grandma's more opened arms; grandpa more next to grandma, maybe kneeing, waiting for hug...; the kids feet make quite a tangent there, just showing a little of girls face)?
Creating visually clearer path of running characters with big bush shapes?
Putting the grandparents characters a bit up hill with overexposed bloomed light behind them to make them more heroic?
A little scribble to see what i mean
