Are clothes considered najis if they are washed together in a twin-tub washing machine, given that some of them have children's urine on them, and what is the correct washing method to ensure purity?

The children's clothes should be placed in a container full of water and wrung out well before washing them in the washing machine with the rest of the clothes. It is better to wash them separately to ensure purity. Although the washing machine purifies impure clothes if they are washed well, what was mentioned previously is more preferable.