Sprinting animation only works when animation reloads?

I have a sprint script that i modified to make it change the walk animation. It works, but it only works when the walk/run animation is reloaded. For example, when running would be turned on while walking, the walking animation stays until you reload it; you can reload it by playing another animation like jumping or idle animation. How do you fix this?

local mouse = game.Players.LocalPlayer:GetMouse()
local running = false
local humanoid = game.Players.LocalPlayer.Character.Humanoid




function getTool()  
    for _, kid in ipairs(script.Parent:GetChildren()) do
        if kid.className == "Tool" then return kid end
    end
    return nil
end


mouse.KeyDown:connect(function (key) -- Run function
    key = string.lower(key)
    if string.byte(key) == 48 then
        running = true
        local keyConnection = mouse.KeyUp:connect(function (key)
            if string.byte(key) == 48 then
                running = false
            end
        end)
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 20
        game.Players.LocalPlayer.Character.Animate.walk.WalkAnim.AnimationId = "rbxassetid://981305988"
        game.Players.LocalPlayer.Character.Animate.run.RunAnim.AnimationId = "rbxassetid://981305988"

        repeat wait () until running == false
        keyConnection:disconnect()
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 12
        game.Players.LocalPlayer.Character.Animate.walk.WalkAnim.AnimationId = "rbxassetid://978520563"
        game.Players.LocalPlayer.Character.Animate.run.RunAnim.AnimationId = "rbxassetid://978520563"


    end
end)