Google+ I shared National Geographic's article about the significance of the summer solstice. The article is an interesting read with a bunch of links to more interesting information sprinkled throughout it. Reading the article prompted me to look at a few resources that could be helpful in teaching students about seasons.
On National Geographic's Education page there are two resources worth noting. The first is a simple illustration of the position of Earth relative to the sun throughout the year. That illustration could support your use of this hands-on activity designed to help students understand the changes in intensity and duration of sunlight on their part of the world throughout the year. Both resources are appropriate for elementary school students.
Mechanism Of The Seasons is a YouTube video that I found. The six minute video could be helpful in a flipped classroom environment as it covers the same information that your students will review in the National Geographic materials mentioned above.