Here are some quick sleep milestones by age, based on information from Healthy Sleep Habits, Happy Child. Remember, every baby is different and these are just guidelines. I followed these more with A, not as much with C, but I still think it is a good reference.
6 weeks to 3 months: night sleep lengthens, early bedtime develops, time between naps is 1 hour to 1 hour 45, naps last 30 minutes to 2 hours, baby starts going from 4 naps to 3
3 months to 6 months: time between naps is about 2 hours, naps last 30 minutes to 2 hours, morning nap develops around 9/10am, followed by afternoon nap developing 12/2pm (12-16 weeks), baby takes 3 naps
6 months to 9 months: time between naps is about 2 to 3 hours, naps last 1 to 3 hours, third catnap disappears, at 9 months baby takes 2 naps
9 months to 12 months: time between naps is about 3 hours, naps last 1 to 2 hours