The answer to this depends to some degree on how we define “children.” The impact of the Internet on a 6 year-old is very different than its impact on a 12 year-old. In general, however, the Internet has both good and bad effects on children.
The bad effects of the Internet are well-known. The Internet can be very dangerous for children. It can expose them to pornography. It can expose them to predators who are trying to use Internet communications to get close to the children so they can exploit them in some way. Less dangerously, Internet use can make it harder for kids to be healthy and to have good relationships. They can spend too much time using the Internet rather than playing with friends.
However, the Internet is also very good in some ways. Perhaps the biggest benefit is that the Internet brings huge amounts of information to children. This can be helpful to them if they have hobbies. It can allow them to find out more about the things that interest them. When kids are in school, the Internet can be of help for school work. If children have to find information about a given topic, it is much easier for them to use the Internet than to find books at a library.
Thus, the Internet can be both a good thing and a bad thing for children.