My 4.5 month old always used to nap for 45 mins in the morning, 2 hours at lunch and 30 mins in the afternoon with usually 90 mins to 2hours between each one.
However he has started doing the 2 hour one in the morning now which is leaving him cranky in the afternoons. Today he got up at 7am, went down for a nap at 8:30am and is still sleeping now. Should I leave him to it or try waking him to encourage him back into his previous routine?