I don’t think I can take any credit for this, but there has been major progress. My young nieces are sight-singing simple melodies.
For years, I had been inventing complex music games for them. The kids had fun, and they excelled at rhythm, but they couldn’t remember intervals. My sister suggested (kindly) that I was probably moving too fast.
This year, we just stuck to singing combinations of do-mi-sol for several weeks. Then (at their request!), I wrote down the same combinations on music paper. They were able to read them instantly with almost no effort. How cool!
Children are just miraculous.