Could you please correct my English sentences?

Many people may envy bilingual speakers because they can speak two languages fluently. However, I think that learning two languages to become bilingual in early childhood is not good idea. There are two reasons why I think so.
First, according to the Internet PAPIMAMI (https://papimami.jp/167/), there is case where children cannot develop both two languages. Sometimes, there are children who mix two languages and speak strange language.
Second, there is a possibility that bilingual’s ability to think is not developed compared to monolingual. When humans think something, almost all of them don’t think by sounds or shapes, but languages. Therefore, if they have not developed language, their ability to think can be undeveloped (cf. https://ijuusya.com/bairingaru-n...).
I do not think that bilingual is bad, but I think that it is good for children to learn only one language.