Is it permissible for me to move to another job with a lower salary, even though the new job is closer to my specialization, but I have a newborn and fear that my income will be affected?

We ask Allah to choose for you what is best. If the salary difference between your previous and prospective job is significant, it is better to remain in your previous job due to your familiarity with its details and the people in charge. However, if the difference is slight, there is no objection to moving. Before all of that, we advise you to perform the legal Istikhara (prayer for guidance).