I assume it's not counting stillborns, otherwise where can you possibly draw the line?

> Child mortality in rich countries today is much lower than 1%. This is a very recent development and was only reached after a hundredfold decline in child mortality in these countries. In early-modern times, child mortality was very high; in 18th century Sweden every third child died, and in 19th century Germany every second child died. With declining poverty and increasing knowledge and service in the health sector, child mortality around the world is declining very rapidly: Global child mortality fell from 18.2% in 1960 to 4.3% in 2015; while 4.3% is still too high, this is a substantial achievement.

Half of all kids in Germany died, less than two centuries ago!

2. In the developing world, it's 0.4%, in the US it's higher at 0.7%. There's some debate over whether that's due to differences in definition, or crap health system and huge inequality. Given the bad health outcomes in the US generally (eg life expectancy), I lean towards the latter hypothesis.

EDIT to add sources, and typos:

https://ourworldindata.org/child-mortality

https://data.worldbank.org/indicator/SH.DYN.MORT