Will the deceased be held accountable for his children's illicit use of the internet or television, knowing that he was the one who brought these devices into the home?

Every good deed you perform to draw closer to Allah and dedicate its reward to your father will benefit him. Charity given on his behalf reaches him, and it is among the best ways to draw closer to Allah on his behalf, especially ongoing charity (sadaqah jariyah). One must be careful not to use what the deceased left behind for unlawful purposes, fearing Allah's wrath and lest the deceased incur sin because of it.