I'm a father to two little boys and tracking their growth is typically done on paper charts such as https://www.cdc.gov/growthcharts/data/who/GrChrt_Boys_24LW_1... which are not very usable on screens and require you to draw lines with pen on the paper for accurate tracking.
So I made a digital version instead with React and D3.
The charts are limited to those for children under two years of age since growth charts for older children differ based on nationality.