two things i just thought of then
Notice they didnt throw sparlock in their home waste bin. Or even their outside wheely bin. They put it in a dump master bin.
They must have walked to find one so that he could continue demonising the house from inside their bin.
Secondly, notice how the mother made her son throw it out. When my parents didnt want me to have something they would take it away and throw it out when i wasnt looking. But this bitch makes the poor little boy be the one to throw his magical little friend in the bin. Therefore he may feel guiilty and he was made to feel it was HIS decition and HE did the actual act of throwing it out. When he tells his friend (who gave him the gift) what happened to sparlox he will have to say "I threw it out" not "mum threw it out"