The only thing I can think of given they go to daycare especially.. what does their daily diet consist of? Do you send them with a water bottle? (No juice unless daycare provides or pack a juice box for PM snack) & no milk besides with lunch. Are they drinking milk after daycare/ your work day? This is the only idea I have on getting back to sleeping 7:30/8pm-5/6am Idk their food intake but are they eating enough food/ not too many snacks? This can also cause alertness at bed as they are hungry. Milk dehydrates & causes frequent wakes etc. sorry if I'm off lol, I'm taking my best guess on a blind situation besides sleep issues. Are they sleeping with a night machine? & Is there a camera in their room or do they sleep with you without a camera? Is the camera wifi?
If they nap, I'd cut all naps Your 4yo isn't "being silly", she's going through something ... probably a cognitive development. I know it's hard to have empathy when you're sleep deprived but it actually is important to remember she's not doing this on purpose to annoy you. She can't help it if she wakes. Where do they sleep?
@Manpreet my daughter has not napped since she was 18 months . My son still has a half hour nap .
Are either of them taking naps during the day?