Is it advisable to re-use an old playpen ( five years) passed down from sibling's daughter? Can a playpen be washed or cleaned? I am afraid washing the playpen will damage the materials.

Yes of course! Many things need not be purchased and can be reused. Handwash the materials and dry it. Done, you can reuse it again and its as good as new.

The fabric can be washed. If u are worried just hand wash instead of machine

thanks