Does the dog like baby? Or is dog jealous? Stress, anxiety, territory marking, attention seeking. Could be getting less attention than before baby got here.
Dogs can be emotional too. He may love the baby, but if he notices the baby getting too much attention and it's a consistent issue over time, he may have done it for attention. I would definitely keep the dog away baby's things when possible and try to give more attention to the dog as best as you can.
could be a sign that they are marking them as their territory.