How can I find the children of children?

The proper name for a child or child of child or &c is descendant.

To do this, we require recursion upon Children.

The observation that we make is as follows:

A descendant D of O is either

• a child of O, or
• a descendant of a child of O.

That is, the descendants of an object are the combination of the descendants of its children and its children.

function getDescendants(object)
    local descendants = {};
    for _, child in pairs(object:GetChildren()) do
        -- `descendants` of `object` are:
        -- children:
        table.insert(descendants, child);
        -- and descendants of children:
        local descendantsOfChild = getDescendants(child);
        for _, des in pairs( descendantsOfChild ) do
            table.insert(descendants, des);
        end
    end
    return descendants;
end

Link: http://wiki.roblox.com/index.php/FindFirstChild Answer: Thing:FindFirstChild("Part", true) --True means if search children of children.

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