Disappearing chicks!???

[BubbaBubbles]

Woo.. where to start. Alright.
My Dutch bantam, Bambi, hatched 6 chicks a couple of weeks ago and has been an awesome mother at teaching and protecting them. Last night, my sister found two chicks on her front porch, possibly from her hen, but the hen wasn't anywhere to be seen. She asked if we would take them, so we did! We get home, it's nighttime, and I went out and gently scooted the 2 new chicks underneath mama Bambi. She didn't really budge, but when checking a couple of minutes later, she was still sitting on them. I had high hopes she had accepted them.

I went out this morning to check and... They weren't there. Bambi was already out foraging with her older chicks, but the 2 new ones weren't with her. I checked the nesting box, under the chair that sits to the side, the palette, under the plants... Nothing. There were no sounds of distressed chirping or any other noise. All the chicks were making content squeaks and trills. I just came in from checking again - still nothing. I even dug around in the pine shavings and behind the coop. Still nothing. I thought that maybe Bambi was somehow carrying them under her wings, so I tried to pick her up - nothing was under her wings, either! There are no feathers or blood or body parts, so I'm completely lost. Now, we do have a rat problem and are still actively trying to catch it. But the holes it had dug had been filled, and there was no sign of entry at the coop door. Again, no sounds of distress.
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WTH happened??? It's 54°F here, and we've never had a snake problem, so I can't imagine they'd suddenly show up. (Anything is possible, I guess.) I also can't imagine it's foxes because they're not that common in our area. And we do have skunks, but there was no sign of a skunk. No paw prints, no fur, no smell. Can anyone help me understand what in the world happened??? Pics below of the chicks.

^^ Pic of the chicks she hatched herself + the coop.
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^^ Pic of one of the new chicks​

 

[sourland]

I would guess that the hen realized they were not her chicks, pecked at them, and they went looking for their mother.

 

[Poultrybonkers]

They probably ate them.

 

[McChooky]

You can't add just add chicks to a broody with 6 week old chicks .
At 6 weeks most hens have already started weaning their chicks
How old were the ones you added? I hope they both escaped

 

[Yardmom]

You can not expect a hen to accept other chicks after her own chicks are a couple weeks old. If she did the unexpected and accepted them, the younger chicks would still be left behind when Mom and the older chicks headed off to forage. The younger chicks would need to take warm up breaks that the older chicks no longer need. Unfortunately if the chicks don't get warmed they do not survive.

 

[McChooky]

You can not expect a hen to accept other chicks after her own chicks are a couple weeks old. If she did the unexpected and accepted them, the younger chicks would still be left behind when Mom and the older chicks headed off to forage. The younger chicks would need to take warm up breaks that the older chicks no longer need. Unfortunately if the chicks don't get warmed they do not survive.

"Now, we do have a rat problem and are still actively trying to catch it"
(Edit)I misread the post and see she added NEW chicks Oh no!

Most broody hens abandon chicks added that aren't close in age but others kill them.The fact that these chicks weren't found makes me believe rats ate them(or the chickens)