Everything that becomes najis with urine, washing it once is enough. As per Ayatullah Sistani, washing it the second time is based on ihtiyat e wajib (obligatory precaution) however you can refer to Ayatullah Khamenei and other maraje who say washing it once is enough.
In regards to gifts given to the child, under the supervision of the father, it can be used for the child or in any other way you see fit so you can sell it or whatever else you find best