Hi @Mouad1307
I’m sorry to read that your son is unwell.
Your right to stay depends on the nationality of your son and his residency status if not a German citizen. The rules are different depending on whether he is a citizen of Germany, an EU country, or another country outside the EU. As a result, your right to a residency permit in Germany can vary between a full right to this to only in exceptional cases to prevent an extraordinary hardship.
Separate to the right or otherwise to a residence permit is the question of not having come to Germany with the correct visa for family reunification. In some case, it is possible to have an application processed in Germany even if the person did not come with the correct visa. This is when it would be considered unreasonable (in German this term is ‘unzumutbar’). In cases where it involved the parent of a baby or small child, then it is generally considered unreasonable to require the parent to leave to get a visa. This is because a lengthy visa process would mean a separation from the parent which a young child could not understand.
This rule is in section 5, part 2 of the immigration law (Aufenthaltsgesetz):
These requirements may be waived if the prerequisites qualifying a foreigner for the granting of a residence title are met or if special circumstances in the individual case concerned render a subsequent visa application procedure unreasonable.
https://***.gesetze-im-internet.de/englisch_aufenthg/englisch_aufenthg.html#p0096
Here is an article (in English via online translation) about the reasonableness or not of a visa procedure in such cases:
https://***-rechtsanwaltskanzlei--oeztuerk-de.translate.goog/zumutbarkeit-der-nachholung-des-visumsverfahrens?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
Best,
Éanna