According to Osho, a child and a Buddha share the same freshness and wonder, acting from not-knowing; but the child's innocence is natural, unearned and destined to be lost, while the Buddha's is the second innocence, regained through suffering, experience and awareness. The Buddha is a twice-born child: innocence transformed into wisdom, conscious, mature, and irreversible.
A child is pure because they don’t know yet; a Buddha is pure again after fully living and understanding, so the purity is wise and never lost.