Sheriff Lindsay Foulis said the 20-year-old exposed her son to potentially tragic conditions by "completely neglecting him".
The toddler was found freezing cold, wearing socks soaked through with cat urine in a house strewn with rubbish and cat litter.
Sheriff Foulis said: "In this day and age, when contraception is no secret, there is absolutely no excuse for her. If you are ill-prepared to have a child you take steps so that if you engage in sexual relations you don't then conceive."
Perth Sheriff Court heard how the defendant "willingly handed over" her son to social workers.
She pled guilty and must do 200 hours' unpaid work.