Yes, it's true cases have risen when we've started to relax restrictions (i.e. open up restaurants, pools, theaters, gyms, etc.).
To expect that they wouldn't rise at all is unrealistic.
But, it's the price most of us are agreeing to pay. In your example, it was for the economy and for people to have jobs.
Now, the next step is for kids to be able to effectively learn and socialize once again. And, there will be some price to pay.
But, when assessing that risk, many think it is worth it.
Especially when you look at the numbers, and even see that the numbers that you reference, which have risen, reflect very low case numbers among children (5% 0-17, 0 deaths).