You've already got the link to information about exposure.
Another really important topic area is composition and the elements of design. Composition is a huge area that encompasses all the subtleties of exposure, contrast, framing, leading lines, depth, and so on. And another really important area, especially if you're wanting to capture people, is posing.
Either of these topics is bigger than what could be easily posted into a thread. I'll touch on one of my pet peeves and then point out a book or two.
Don't shoot down at your subjects... Sorry, that's just my thing. Psychologically, I think that aiming down towards the person is to put them at a lower stature than you or the viewer of the photograph. Get down on a knee or otherwise scrunch down to capture the kids at eye level. You did that for the reptile, but not the kids. There are plenty of exceptions to this or any other rule, but that's just an opinion that I have.
Now, one advantage to shooting more at eye level is you start to get more interesting backgrounds than just the ground or furniture. As an example, in the first picture, there's a distinct line between the sidewalk and the ground cover that leads right into her head. Plus there's the blue chalk/paint mark on the sidewalk too. These don't help your portraits.
If you're the type to pick up a book, then I like "The Photographer's Eye" by Michael Freeman. It talks about many elements of composition. There are many additional books, with some being deeper or more advanced in the concepts.
Also, there's another website with lots of tutorials about using your camera that would be good to review:
Photography Tips and Tutorials for Beginners
In the meantime, think "backgrounds" and "direction of light" when you take pictures. Developing that habit will likely serve you well for all types of photography going forward.