Before entering a church, explain one thing: whose tomb is here, what happened here, or why pilgrims come. Invite children to choose someone to pray for, notice a symbol in the art, or ask their own questions. Keep quiet moments appropriate to their abilities and respect the worship of others.
Use genuine local resources when available. Lourdes operates the Little House of Bernadette and a Youth & Family service; Fátima publishes an age-adapted program, but the currently described program is in Portuguese and requires advance arrangement. Check both directly before promising them on a departure.
A parent may need to step outside during a long Mass, Adoration or procession. Food, play and downtime do not undermine a pilgrimage; they can help a family participate in the rest of it.