Parenting and worry

I've decided parenting is hard. I want to do what's best for my kids but honestly that's hard. My son (J) spends most of his time at his dads (don't worry about why) so when he is with me I want it to be fun. I will tell you right now sometimes it's not fun. I haven't figured out the balance yet of being a fun mom and a mean mom. I have decided I want to learn more about love and logic. In a nut shell you give your child choices and learns from the consequences of those choices. It is so hard to watch him make the wrong choice but he has to learn. For example he got a balloon from a fair. I asked him "do you want me to hold it or do you want to hold it. he held it, dropped it and it popped. I knew that was going to happen and it broke my heart to see him sad about it, but it learned. Another example would be. I asked him if he wanted to take a bath by himself or if he needed help. He was fighting me so bad on taking a bath so I said "ok i will help you and put him in with his clothes on. Occasionally I will ask him if he remembers these times and he says yes. I haven't figured out if it's good he remembers that sucky time in his life or if it's good because he remembers he learned from that. Changing the subject a little. Little girl is 6 months old. She can sit up but I think she is traumatized because she fell over and wont do it now. Someone told me that she might be a little behind because she is little. I don't want to say "she's little so that's why she doesn't do that." I think that's garbage. I've seen kids that are super premature but still hit all of their milestones at a "normal" time. I don't want to push her though. It's all about finding balance. Am I the only one who worries about this? I don't ever remember worrying about J's development. I've heard about early intervention that if you notice your child is "behind" that you can help in the beginning so it's easier for the child. Am I going to need this? If so how will I know? Confusing!!!