Hi there..... this is a classic sign of 2-1 transition (there are so many of us going through it at the moment
).
I would say that the NW are caused from overtiredness. Its really really hard to increase A time all in 1 go at 12months and I did the exact same thing... I was waiting for Isabella to get "used" to it, etc... but the NW just got worse and more frequent so I had to go back to 2 naps....
During the transition, its a case of 2 is too much and 1 is not enough. They almost need 1 and 1/2 naps... so ALOT of us (yes, I'm going through it all over again) have been cutting the morning nap to 45mins and offering the afternoon nap about 3.25-3.5hrs later and then bedtime about 3.5-4rs (max) later. My lo can handle 3.5hrs in the afternoon and 3.75hrs before bedtime so it might be a bit of playing around.
If you are finding that he is finding it really hard to stay awake till 11.30 then don't push it. I am sure that daycare can try and offer him 2 naps... there are always ways to work around it....
This is the routine I would aim for:
6am - wake for the day
9ish - morning nap (wake after 45mins)
1.30-2pm - afternoon nap
6.30ish - bedtime
I would have a chat to mum and tell her how important it is not to let him stay awake for as long as he wants/can becuase your lo might not show tired signs and infact could be very tired.....
If he is falling asleep at 10, then get mum to wake him up 30mins later and offer the pm nap 3or so hrs later....
If you absolutely have to keep him awake and he only manages 1 nap for the day, then bring bedtime forward... as early as 5.30 (if he's had like 5hrs A time in the afternoon). Making bedtime earlier should help with the NW....
Layla