I do have a kid and I'm pretty sure children aren't manipulative at all at 3-4 months old. They just operate on immediate needs and instinct. Manipulative behavior starts at around 1 year old, beliefs of small infants being manipulative are typically just projection (you feel angry because your baby wakes you up every 2 hours, so you think it's manipulating you, and that makes you feel better about being so angry).

Of course they are good at getting attention, but that's because they need attention. That's why nature gave them the ability to cry surprisingly loud from the moment they're born.