I think this is a better question for a chicken forum not here.
My family has raised chickens for more than 14 years (since before I was born)
I would say BAD idea. Doing something without your Mom’s knowledge (other than a surprise present) is always a bad idea.
As far as actual care goes I hope you did/are doing a lot of research. You will need a heat lamp because they need a temperature of 95 degrees Fahrenheit.
You will need something to keep them in that is safe to have under the heat lamp that is big enough for them to have plenty of room and for food and water.
You will need chick feed and a waterer that they won’t drown in (that does happen more often then you’d think).
I hope you live somewhere roosters and hens are aloud because even with “guaranteed” hens it is still 50:50 for a rooster.
You need a predator proof coop for when they get older and be prepared to clean it.
You somewhere safe for them forge in outside where they get killed by hawks or stay cats.
They will also need a nestbox to lay eggs in.
They (adults and chicks) stink, make a giant mess, are loud, and eat A LOT. I highly doubt you will be able to keep them secret long.
If you can’t provide this stuff they will die or live in horrible condition.
I would definitely say BAD idea considering all this.
I’m not trying to sound mean or rude just make sure that you know what you are getting into.
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Picture to demonstrate size of coop.
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Picture to represent size of coop.
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Chickens coming out of roost after being locked up for the night.
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Picture to demonstrate size of coop.
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Picture to demonstrate size of coop. We have ours under a Weeping Willow to prevent hawk attacks.
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Picture to demonstrate nestbox. Broody (hen who tries to hatch eggs) with her chicks.