How do I build a child's bedroom?

You can make a bedroom by making a bedroom wing or using the left side of the upstairs room area. You will need some sawn logs and nails to do this. you can buy 20 sawn logs for 200 gold from any lumber mill owner. You can craft nails using a forge or an anvil [if you made the one in back room of the house, otherwise, use the anvil outside]. The bedroom needs to have your beds, the kid's beds, and a container near the kid's beds [child's chests in bedroom wing, drawer in the upstairs room]. You might want to furnish the rest of your house so your kids can move in. You might want to buy more materials at trading store such as:

Riverwood Trader- Riverwood

Belethor's General Goods- Whiterun

The Prawned Pawn- Riften

Arnlief and Son's Trading Company- Markarth

Sardi's Used Wares- Windhelm

Bits and Pieces- Solitude

Gray Pine Goods- Falkreath

If you haven't built the bedroom wing, make sure you use the drafting table to "plan" it and use the carpenter's workbench to build the exteriors.

Ugh while it's hard to understand what your saying, I believe it's the west wing but it needs certain resources you can only buy in certain shops such as the riverwood trader, belthor's general goods, and gray pine goods.

You must make 2 child beds and 2 child chests even if you are only adopting one child