We moved DS to the seat at around 3-4 months (forgot exactly when!!) after he *decided* he wanted to see more. He had excellent head control from birth but we kept the seat in the reclined position until about 4 months when he could maintain it for longer and then moved it to the next more upright level. The main issue with putting them in the seat early is making sure the restraint straps are secure and they can't slip their arms from under them.