A deeply poignant work written by Nin to express solidarity with Spanish war victims. It is distinct for its hauntingly simple melody and sparse, evocative accompaniment that builds into a powerful climax.
The challenge lies in the control of the voicing in the middle section as the volume intensifies.
Comparable difficulty and character — good candidates for what to learn next.
Canto de cuna para los huérfanos de España is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 8.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Canto de cuna para los huérfanos de España lasts about 5 minutes.
Canto de cuna para los huérfanos de España is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Pavane pour une infante défunte by Maurice Ravel, Berceuse héroïque by Claude Debussy, Canon by Sergei Rachmaninoff — see the full similar-pieces list on this page.