The line graphs show the average money British parents spent on sports activities of their kids each month as well as the number of children who took part in football, athletics and swimming from 2008 to 2014.

Overall, it is clear that the money spent by British parents on their children’s sports increased over a period of 6 years. Additionally, football was more popular with British kids than athletics and swimming.

According to the first chart, in 2008, British parents spent 20 pounds per month so that their children participated in sports activities. This figure went up gradually over the following six years and peaked at 30 pounds in 20014.

In 2008, there were about 8 millions of children in Britain played football. The number of kids participated in football declined slightly in 2010, and then grew marginally between 2012 and 2014. By contrast, there were only about 1 millions of British kids took part in athletics in 2008. However, a sharp increase was recorded in the number of children played athletics from 2010 to 2012, and it hit the highest point of 5 million children in 2012. Finally, this figure for students in swimming was nearly 2 million in 2008 and it gradually rose in the next six years.

letu96kids

"Kids" is somewhat informal. Use "children" for IELTS Academic purposes.

letu96average money

In fact, it is the average amount in pounds sterling .

letu96as well as

Why not simply have two sentences, one for each graph? Or join with 'while': while the other graph shows ....

letu96over a period of 6 years.

over the six-year period. Must be 'the' to reference the period already mentioned. 'A' period leaves the reader wondering which period.

letu96 increased

Increased how and by how much? Increased steadily and substantially

letu96football was more popular

What about the fact that athletics overtook swimming? Surely this is a significant development?

letu96According to the first chart,

Once the charts have been properly described in the introduction, there is no real need to refer to them again.

letu96spent 20 pounds per month so tha

"Spent ..... on" is the natural collocation. .... spent twenty pounds per month on their children's sporting activities.

letu96The number of kids participated in

the number of children participating in

letu96there were only about 1 millions of British kids took part in

... there were only about one million British children taking part in ....

letu96the number of children played athletics

the number of children doing athletics...

The verb changes according to the sport. We play football, go swimming, and do athletics.

To me, the detail paragraph should emphasize that:

1) Football participation was much higher than the other two, but has not grown substantially.

2) Athletics started with the lowest participation, which then rose steeply between 2010 an 2012, and subsequently flattened off, ending above swimming.

3) Swimming participation rose steadily throughout the period, but had been overtaken by participation in athletics by 2011.

There is a model answer for this task here:

https://ielts-simon.com/ielts-help-and-english-pr/2016/09/ielts-writing-task-1-separate-line-graphs-answer.html