I always get nil from this table, can you find my mistake?

To explain what's going on, I'll briefly explain how tables work in Lua.

Lua tables have two parts to them: a hash part and an array part. The array part contains the values of the table that are indexed using positive integers (1, 2, 3, etc.). The other part is the hash part, which can be indexed using any Lua value other than nil. Most commonly, strings are used for indexing it, but they could also be userdata or tables.

In your case, you're writing to the hash part of the table, but you're trying to find the values from the array part. v.Name is a string, so it goes the hash part, while keybinds[1] tries to index the array part. Instead, to check whether a table contains any values, including both the hash and array parts, you can use next, like so:

print(next(keybinds)) --> prints `nil` if and only if the table keybinds is empty

Side note: next is an iterator function, often used for going through tables in for loops. The two following loops are actually functionally equivalent!

    for i,v in pairs(KB:GetChildren()) do
        keybinds[v.Name] = v.Value
    end

    do
        local tab = KB:GetChildren()
        local i, v = next(tab)
        while i ~= nil do
            keybinds[v.Name] = v.Value
        end
    end

Edit: Changed "numerical part" to "array part".