Well, like with all figures, opinions will vary, but for an actual infant I think the Cubed Babies are really the only option.  They are based on the P4 infant, so are definitely showing their age, but not shiver worthy. 

Milbaby3 and the older Milbaby are pretty scary and don't do anything under a toddler very well, I did see one render once where it was used as an infant well.  K4 toddler isn't compatible with Poser and I don't think Apollo does anything less than a toddler very well.  We really don't have any options for newborns when all is said and done.