You can put poison in their food. It will take them longer to die because they will eat it. But it is very quick and humane. I would use a poisoned mouse trap if you can find one. Otherwise, you can try making your own. Get an empty plastic bottle (or other wide-mouth bottle) and a funnel.
Put the funnel in the bottle with a small amount of the poison in the bottle. The bottle should be closed tightly. You can leave the bottle in a dry place. You will know when the poison works because the mice will not eat the food in the bottle. They will find some other way to get it. You can also try using a spray bottle.
ou can buy the poison from your local hardware store or pet shop. There are many different kinds. You can also make your own poison. Use a mixture of salt, pepper, garlic, onions, and hot peppers. Mix them together and put them in an empty bottle. Do not use anything that will burn or sting you. You can also put some of the mixture in a cup with water. The mice will drink it and die.