Easy solution to this problem... Just toss a couple of dead bugs under the sheets before the kids get into your bed and let them see them ! You can say “I don’t know why all these bugs keep getting into the bed ? I think they are invading my room “ ! The kid(s) will never want to sleep with you again...
Meh. My daughter had a live scorpion in her room last night. She found it on the floor when she was using her little book light to find a dropped chapstick cap.
Once the scorpion was dispatched (by me, of course), she went right back to bed.
She's six.