I have insulation coming out of my air vents?

In my bathroom and bedroom air vents there is pink fluff coming out of them. Could this be insulation? Is this bad to breath in? I have young children and don't want us getting cancer or something over it. The air ducts run under the house and the vent is on the floor.
Update: Thank you I feel better now, Im trying to get someone out to check it out but for now I was worried ... i thought I heard something chewing in the middle of the night a while back but have not heard anything. So that's what i was thinking too a mouse chewing on it... great thanks little guys lol ..
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