10 month old- sleeping just got worse

[Firstty]

She was sleeping through most nights with maybe one or 2 quick wake ups but now won't go to bed til 9, wakes up around 12 and takes a looong time to get back down. She's then up at 4.30-5ish for the day.

I've just gone back to work and she's very settled and happy at her childminders but has long naps there (2-3 hours in the morning and maybe another hour in the afternoon). Do I get them to start cutting her naps short? Anything else that could be causing this?

That does sound like an awful lot of napping. I'd start with that...maybe get the CM to start to encourage a couple of hours after lunch and just a short cat nap in the morning to get her through. I would expect that to start to make a difference.

She is maybe going through a developmental leap and think there can be a bit of a regression there sometimes. My son is 10 months and we've has some crappy issues with his sleep lately too.
Im also just started back to work but have the opposite problem where he barely naps at all at childminders, he only slept 10 mins in total yesterday! Although thankfully he slept all night last night!
Maybe the morning nap needs cut by an hour or so.