"Everyone's children participated in the holiday."
Translation:Ĉies infanoj partoprenis la feston.
Festo can mean a religious holiday, celebration or a party, depending on the context.
Yes, there are two ways of saying it:
Partopreni en la festo.
Partopreni la feston.
I couldn't find partopreni in the dictionary, so I looked up the parts... parto= part preni=take partoprenis = took a part? A funny way to convey participate.