Relationship with infant stuck / grow really slow.

relationship with my infant does not improve. when he was born i instantly age him up because i don't like gameplay with newborns. and relationship bar with both oh his parents stuck on a middle ("friend" level). my sims take care of him and fulfill all his needs, but relationship bar is still stuck. well, actually, it is moving, but VERY slow. i made some friendly actions towards infant, but it increased juuust a bit, so it barely noticable.
then i hired a nanny service and she gained full friendship bar with my infant in couple hours. what is wrong and why the infant hates his parents so much? :D how do i fix this?