Is it obligatory to inform the school about the pregnancy, considering that they did not explicitly ask about it, but rather inquired about having children, and disclosing the pregnancy might affect the chance of getting the job?

If the school stipulates that a teacher must not be pregnant, then one must adhere to the condition and inform them of the truth of the matter. They have the right to accept or refuse. One must not conceal the matter for fear of rejection, because sustenance is predetermined. However, if they do not stipulate this, then there is no obligation to inform them about the pregnancy.