I think your post highlights the challenges of working in any demanding career on a less than full-time basis. Presumably before you had your child you accepted the demands of the environment, and the hours, as part of the job that needed to be done.
I think you are fortunate that your boss has agreed that you could work part-time and that your hours could be fixed, if that is not the normal pattern of the job. Some employers would have rejected your proposal citing business need. I am not saying that this is right, just that from what I hear it is unusual, particularly in media jobs.
Your colleagues probably find it a little frustrating that they have not been able to negotiate the same terms. The time may come when some of them also require part-time contracts, and then perhaps they will show more understanding and may even be glad that you have established a successful pattern.
When I first went back to work my boss and my male colleagues were extremely doubtful that my job-share arrangement could ever work. It took a long time to change their minds, but the proof of the pudding was in the eating - hard work, persistence, unfailing cheerfulness, some flexibility on my part (luckily I could do that), smiling at people when I wanted to spit at them for their ignorance, and output that was higher than any of the full-time staff.
So you may feel a bit despondent at the moment, but you are in a job you have trained for, you are at least taking home some money, you are keeping your skills and contacts up to date, you have negotiated something that suits you in a very difficult industry, and you are spending time with your little boy. Keep your chin up.