Final answer:
Children aged between 6 and 12 gain on average 3.2 kg (7 lb.) per year, grow 5.8 cm (2.3 in.) in height annually, and by age 12, they typically weigh around 41 kg (91 lb.) and stand about 150 cm (59 in.) tall.
Step-by-step explanation:
The average yearly weight gain for children between 6 and 12 years of age is approximately 3.2 kg (7 lb.) per year. During middle childhood, which encompasses this age bracket, children also grow about 5.8 cm (2.3 in.) in height annually.
By the time they are 12 years old, the average child weighs around 41 kg (91 lb.) and has a height of approximately 150 cm (59 in.). These figures illustrate a slow and steady growth pattern, with the mentioned weight gain partly reflecting an increase in muscle mass when compared to earlier years.