I’m a visual learner so it’s easier for me pick up things by seeing them, which is why I’m going to direct you to look up lifestyle blogs, kid photographers, etc on Instagram, Pinterest, or Google. Looking at tons of photos you’ll be able to see what works and what doesn’t and what’s appealing. Then try to mimic what you like. Take tons of photos yourself because that’s really how you develop your eye.
As for lighting, you don’t need to invest in any lights just yet. Natural is the best way to go for what you have in mind, imo. Though a reflector with scrim and flag would be good to have.
YouTube is a great place for tutorials if you need help learning your camera. Search your specific model.
If you’re really serious about photography, don’t be afraid to post photos and ask for critique.
You do test prints first so you know how/what to adjust. But since you’re outsourcing your printing it’s a guessing game. If you know this particular printer prints dark, adjust accordingly.