26 month old suddenly waking at 5.30am

[LCF2021]

My 26MO DS has gone from religiously going 7.30-7.30 with a nap from 1-3pm to now waking every morning at 5.30/6am. In need of some possible tips to help shift his wake up time back, I appreciate we may not make it to 7.30am again but even if he could manage 6.45/7am. It’s been going on for 3 weeks so we’ve tried changing his routine; cut his nap to 1.5hrs for a week with no change, then to 1hr and didn’t see a difference. He’s been chewing his hands and dribbling a lot so I assumed his top molars were coming in but surely that wouldn’t affect him for so long.
He’s also waking up upset at 5.30am, it doesn’t seem as though he’s had enough sleep and wants to get up. Now he’s up so early I’ve had to bring his nap forward to midday which means he’s generally not making it until 7.30pm bedtime.
Worth mentioning we have a 5 week old DD who my son is besotted with so I wondered whether he’s waking early as he wants to see her.
Any tips or advice or do we just ride it out? He went through a tricky separation anxiety and sleep period about two months ago which thankfully resolved itself before baby arrived.

Waking early mornings can be caused be the two extremes:

• Overtiredness causes early morning wakes because this is the time when sleep is lightest. An overtired baby tends to be restless in the light sleep phase, causing them to fully wake. Solution would be more sleep over 24h

• Undertiredness will similarly see early wake ups. As toddlers get older they naturally move away from 12h overnight sleep down to 11h and then 10h. Its reasonable to expect that toddler still needs a daytime nap (can't do 8h plus awake in one go), so stopping/cutting the daytime nap often isnt effective. Solution would be later bedtime.