You can do this:
while true do
for a, sound in pairs(script.Parent:GetChildren()) do
if sound:IsA("Sound") and workspace.Map.SoundRegions:FindFirstChild(sound.Name) == nil then
sound:Stop()
end
end
end
:FindFirstChild() returns nil if it doesn’t find the child, returns the child if it does.
Your code is also terrible performance-wise and functionality-wise. I suggest you use the ZonePlus module to detect whenever a player enters and exits a zone, it’s pretty great.