If you think it most likely that they will use it in haraam ways, it is not permissible for you to allow them to do that, because that comes under the heading of helping in sin, and Allah, may He be exalted, says (interpretation of the meaning):
Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment
What we advise you to do is put accessibility to the internet solely under your control, so as to avoid any doubt and to have peace of mind and not worry about being responsible for anyone else. It is rare for a person to use the internet without falling into objectionable types of use.
And Allah knows best.
Reproduced from Islam QA