I've hesitated on crocheting cat toys due to safety concerns. Claws may get caught in the threads of the yarn and yarn can be eaten and cause blockages. If you do crochet toys for them, I'd consider using yarn thats made of one solid thread rather than traditional yarn, like the velvet blanket stuff. I've seen small balls of thinner velvet yarn at dollar general before that might be perfect for it.
Also, don't give them the toys unattended, and always remember to throw them away the second they start unraveling or breaking. I worked at quite a few vets offices as an intern and a tech and saw many people come in with animals with intestinal blockages who were shocked because they never saw their pet eat anything odd. Hair ties, string, and parts of toys are big ones for cats to eat. Catnip inside may encourage them to chew or eat the yarn.
I know it sucks because you want to make cute toys for them as a way to show love, but unfortunately cats can be dummies. We still love them anyways!
I've been crocheting on and off for 2.5 years now. I tend to go through periods of crocheting all day every day and then switch to a total lack of interest for months. I started when my husband and I were super poor and looking for hobbies to do together. We got two balls of yarn, a cheap set of knitting needles and two crochet hooks. We tried knitting first and didn't like it. We switched to crochet and it clicked for me. Now I love making amigurumi as I can't stand making bigger items where I have to count stitches. I'm starting to freehand things and am hoping to maybe learn to make patterns myself.