EBay is unlikely to send you random messages about for adult sex toy products. Their targeted messages are based on members' viewing or buying history.
If sharing a computer with your family, it wouldn't be exactly unknown for children to have explored adult items when no-one's around!
If your children haven't been peeping, you could have unknowingly downloaded some malware. This will be placing unwanted ads on your screen, typically for porn or get rich quick sites. To get rid of this, download and run a malware removing tool, like malwarebytes-antimalware.
