Is it permissible to donate dolls and children's clothes to an orphanage, knowing there is a possibility they might be sold, and is the donor sinful if adults use them or young people wear them?

There is no harm in donating dolls and clothes to an orphanage. Doubts do not preclude the permissibility of donating them, and there is no assistance to the unlawful in doing so. If anything questionable occurs, there is no sin upon the donor.