These days children see far too much violence on TV and this can affect to their emotional development.
While it was correct to use affect (verb) instead of effect (noun), the preposition is not needed.
X affects Y (without ‘to’) / Y is affected by X:
Students also sometimes write affect on, possible because they are familiar with the phrase have an effect on. However, no preposition is needed here, either. Both of the following are possible.
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