The Ramayana is structurally simpler than the Mahabharata. One arc. One question. But one arc doesn't mean tell it in order. Children meet the Ramayana in moments, and the order of those moments matters more than parents think.
Start with Hanuman, not Rama
Hanuman is most children's first real door into the Ramayana. Loyalty, mischief, magic, flight. Children meet themselves in Hanuman before they meet anyone else. Rama as the quiet, steady centre arrives through the people around him. That's the right order, even if it isn't the chronological one.
Some traditions actually begin this way. The Hanuman Chalisa is often a child's earliest contact with the Ramayana, long before the full epic is read.
The five doors that work for ages 3 to 5
Hanuman lifting the mountain to find the herb. The squirrel rolling pebbles to help build the bridge. Lakshmana drawing the line that must not be crossed. The boys' childhood with Vasishtha and their bows. Jatayu's bravery against impossible odds.
Each of these is small enough to fit inside a bedtime, big enough to live in a child's head for a week. None of them require the full plot to make sense.
Where to leave a gap (for now)
Sita's abduction isn't where the Ramayana begins for a child. Ravana's death isn't where it ends. Sita's trial by fire, and her later exile, are some of the moments parents ask about most and find hardest to handle. They land best at ages 7 to 9, after years of friendship with the characters has done the work.
What's different from the Mahabharata
The Ramayana is gentler in its average moment but sharper in its individual tragedies. The Mahabharata is a library. The Ramayana is a single thread you can lose hold of and have to pick up again. Both deserve their own pace.