My babies are growing up so fast

So Sooty, Smudge, Ebony and the gang are now 3 weeks old! I looked at the calendar this morning and realised how fast they've grown - and they are so much bigger - and hoovering through their chick crumb.
They appear to be 2 types...there are 4 quite big plain black ones and the other 5 are a mix of black and white - possibly got some Plymouth Barred Rock in them - we shall see.
By the way, they are inside our house, given the temperatures outside at the moment. This is endless amusement for both Phoebe and Luke, of course. We have a concrete floor in our 'sunken lounge' and the chickens are living in one corner now, which we've blocked off and they have layers of cardboard, newspaper and sawdust to keep them sanitary and a warm light bulb going 24/7 to keep their tiny bodies warm until all their feathers are grown.

This pic shows an amazing animal our Luke is. Is he waiting for them to fatten up? Does he think he's Mum? Are they friends? We are still trying to work it out. For hours he stands on the edge of that ledge, peering over extremely keenly. Now, when he has FOOD in front of him that he can't get to yet, he does what dogs do - he salivates in long slimy dribbles...yet he will do this looking at the babies thing all night and no salivation. Twice he has fallen in, because he was watching so intently, and no casualties. And one evening, when we were out for about 5 hours, I think I forgot to shut the door between him and the chickens properly and he was there standing on the edge when we got home - and I had a panic and counted them quickly, feeling quite surprised to note that there were still 9 chickens cheeping happily from their pen!