system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do so many little kids pronounce the "R" sound like a "W"?

It seems strange to me that there are so many younger kids that can't make the R sound and they just substitute it with a W sound instead. (Think "I'm going wabbit hunting") 

Also there are plenty of kids who never break off this habit and it can follow them all the way into their early teen years.
gpt
Speech-Language Pathology graduate student here. Substituting /r/ with /w/ is common in kids because /w/ requires less muscular control, especially of the tongue. Motor control develops over time, and most kiddos outgrow this by age 5.