Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: When a slave woman bears a child to her master, and after that she is married off and bears children, her children have the same status as her, as slaves, for as long as her master lives. If he dies, they are free.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب عتق أمهات الأولاد / 21800