It is narrated from Sa'id bin al-Musayyib (may Allah have mercy on him) that Umar (may Allah be pleased with him) used to allot a share even for a child once it cried out (at birth).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12975