How can I get X number of children?

you can just use a regular for loop, like this:

local Children = Model:GetChildren() --Replace Model with whatever you want to get the children of
local NumChildren = 4 --Replace 4 with the number of children you want to get

local ObjectTable = {} --This is the table where the objects will be held
for i = 1,NumChildren do
    table.insert(ObjectTable,Childen[i])
end

Note: The objects returned will not be random, and if the model is left unchanged, it will return the same objects all the time