To send an email through Sandbox, you will need to:
Families tab and stay on the Family List page.
From there, you can filter for who you wish to send the email to by clicking on the Filter button. If not, ignore this step.
If you have more than 25 children on this list, you will need to make sure that all children are on one page. This saves you from having to do this a couple of times. To put them on one page, you will need to click on the top drop down and select Show All. If not, ignore this step.
Click on the checkbox on the top blue bar (above the children's names) to select all children.
Click on the top drop down and select Send Email.
From here you can edit the subject line and body. Leave the "Hi [FirstName]" because this will input the first name of the parent based on the email inputted in Sandbox. You can also select Send me a confirmation email which will help you keep record of what you have sent out to parents.
Click Send when you are all done.