Similarly, second hand toys don't really sell at op shops like clothes do.
I don't actually think this is true - in a lot of the op shops I go to the toy section is one of the most popular sections - I personally buy many toys from op-shops. My mum is a massive op-shop toy buyer, people buy a lot of toys at garage sales and kids/baby markets, and often toys sell out at stalls ahead of clothes.

BS - All the op-shops round here will take second hand toys - so it also seems odd to me that you were unable to donate toys. Some organisations only take specific things and if they are giving them out often they have to comply with different regulations to op-shops selling them (E.g St Kilda Mums is one where you can donate a cot for example but it has to meet a set of criteria, a cot that may not meet those criteria can still raise money for charity by going through an op-shop though - or say by selling it yourself and donating the money). But toys in op-shops do benefit those in need, either by them being bought specifically for those children, or by the money they raise for the organisation.

I see nothing wrong with people posting about their children wanting to donate, I don't believe most people do it for any sort of reward but because it promotes it, someone may see it and then do the same.