Why did my dependents receive stimulus checks QUESTION

Everything was based off of 2018 taxes(joint filing) because I filed my 2019 taxes too late to be considered for stimulus. In 2018, my son finished his senior year of high school and became a full time college student in the fall. He earned about $8,000 with part time work. I claimed him on my taxes as a dependent and we did his taxes and indicated he was claimed by someone else(me). Why did he receive a $1,200 stimulus check, is this a mistake? Also, my daughter was a full time high school student in 2018 and she had a part time job where she earned about $1,000. I claimed her on my taxes as a dependent and we did her taxes and indicated she was claimed be someone else(me). Why did she receive a $1,200 stimulus check, is this a mistake? She was only 16/17 during 2018. Ironically, my wife and I only received a $942 stimulus check based on our 2018 taxes.