If the baby is no longer a bassinet it is no longer a object and would need to be carried to each of the locations you mentioned like the stroller and baby swing at that point it would be a Sim all the work would needed done to create this life stage and I say why stop there.
As elanorbreton said if Sims can carry objects pets and toddlers they can do the same for a baby. I'd love it if they would do more with the baby than leave it a newborn till it ages up let it develop babies learn to crawl before becoming toddlers they don't have to be lifeless objects placed object to object the entire life stage.