Min:

I think there are many things that children like me can do to make better environment. First, to decrease the amount of trashes that will throw out right after completing their jobs, we can buy bigger product. For instance, we can buy a big plastic bottle of milk than buying two or three plastic bottles of milk. Making one big plastic bottle uses less plastic than making several of small bottles. Except buying bigger plastic bottles, we can use our own cups and forks in coffee shops. They usually give disposable paper cups, and plastic forks because people dislike to use things again that other people used although they have been washed. But if we bring our own things then, we can decrease amount of trashes and, in some food shops, they will discount the price if you use your own cups. I think these ways are very good to make the environment better.

Better:

I think there are many things that children like me can do to make better environment. First, to decrease the amount of trash that will be thrown out right after completing their jobs, we can buy bigger products. For instance, we can buy a big plastic bottle of milk than buying two or three plastic bottles of milk. Making one big plastic bottle uses less plastic than making several of small bottles. Except buying bigger plastic bottles, we can use our own cups and forks in coffee shops. They usually give disposable paper cups, and plastic forks because people don't like to use things again that other people used although they have been washed. But if we bring our own things then, we can decrease amount of trash and, in some food shops, they will discount the price if you use your own cups. I think these ways are very good to make the environment better.

Explanation:

1. The word 'trash' is already in plural form. It means waste materials or things that are no longer wanted or needed

2.  Please remember this structure when you are talking about a passive subject. [will+ be+past form of verb]

Well done Min!