Is it a red flag for a guy in his twenties go back to the dating pool as a single dad?

Why do people consider it a red flag if a single parent goes back to the dating pool? Or if they're talking to someone and find out the guy or girl actually has kids they'd immediately lose interest?

Is it a red flag for a guy in his twenties go back to the dating pool as a single dad?
Is it a red flag for a guy in his twenties go back to the dating pool as a single dad?
Is it a red flag for a guy in his twenties go back to the dating pool as a single dad?
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