This issue is complexed, but for an international scale- the way you can uphold children's rights is to create fundraisers for UNICEF. This is a UN sponsored NGO dedicated to saving children all over our planet.
On a personal level, you can uphold children's rights by creating youth groups, that volunteer in your community and show youth leadership. It is through these initiatives where you help the less-fortunate, or show adults the amount of work we can achieve as 'children'.