Unfortunately, it does feel a bit like going backwards but I offered my 2yo dd some milk yesterday and this morning when she woke at 5.10ish and she slept til 7am yesterday and then today til 7.30am (although this morning could also have been the lack of usual day nap - brought about because she didn't wake til later).
So maybe they are hungry and are finding it hard to get back to sleep - could try offering a biscuit or something if you don't want to offer milk!