Between 10:00 am and 6:00 pm, head to the Meadow to play in the snow with everyone. If you have a high 5-heart friendship with the people in attendance, you can invite them to build a snowman with you. The number of people you can build with will result in different sizes of resulting snowmen.
1 to 5 people - small snowman
6 to 10 people - medium snowman
11 or more - large snowman
You will raise your friendship a little bit with each person that you talk to, and you'll increase it a lot more if they accept your invitation to build the snowman.
To activate the festival you will need to of unlocked all of the Main charcters, except for your child and the Mineral Town people.
The emulator I'm using isn't perfect, so that's why the options don't come up.
Harvest Moon DS: Island of Happiness Statistics For Sandymaxy
At this time, Sandymaxy has 1,041,566 views for Harvest Moon DS: Island of Happiness spread across 131 videos. His channel uploaded 5 hours worth of Harvest Moon DS: Island of Happiness videos, or 6.74% of the total watchable video on Sandymaxy's YouTube channel.