Yeah, we must consider that babies are basically covered in poo and urine. It’s up to you if you want to introduce that to the kitchen. In the absence of an alternative washing location, I suppose it might be acceptable. However, if you have somewhere else - i.e. bath tub available, that would be a more appropriate choice.
The alternative explanation to appease baby lovers is that the kitchen sink is unsanitary for infants. I don’t know about you, but I regularly put raw meat there.