Originally posted by: ..RamKiJanaki..
In Valmiki, there is an explanation for why Dashrath divides the paayasa as he does.
First, he goes to Kaushalya as she was his chief consort and gives her half of the paayasa. Then he goes to Sumitra and gives her half of the half. When he reaches Kaikeyi, he changes his mind and instead of giving her what's left, he again divides the remaining and returns to Sumitra, giving her what little is left.
The reason he gives the paayasa to Sumitra twice is that he wanted her to give birth to twins, one who would serve Kaushalya's son and one who would serve Kaikeyi's son. He felt this would balance the relationship between the brothers. If there were only three brothers, he feared what would happen if two of them befriended each other and the third became envious. So he wanted Sumitra to give birth to two sons with her qualities, so that in the future, there would be no problems between Kaushalya and Kaikeyi, and their respective progeny.
Dashrath was actually very farsighted when he divided the paayasa. He had Raj neeti in mind and didn't want any politics brewing in his household.