I love Palm Sunday worship services with the Hosannas and the children processing with palm branches at the start of worship. With stay at home orders in Louisiana lasting through April 12 (Easter) we will not be gathering in person for Palm Sunday worship. But we will have online worship!
As part of the remembering the crowds gathering to shout "hosanna" and even the rocks crying out, our plan is to have children and families at home take photos of them waving palm branches (greens from their yards or homemade from paper) and send them in. So for that part of the online worship (we have been pre-recording worship and posting on YouTube), there will be a slideshow of children and families with palms during the opening hymn (rather than just watching the worship leader play guitar and sing). Families be encouraged to have a Bible study of the scripture passage that retells the Palm Sunday story as part of the at-home learning to accompany this activity.
As an alternative, you could assign families a letter in the word "hosanna" and have them make posters and take pictures and send them in, adapting what is suggested in this lesson: HOSANNA acrostic presentation.