What is fair?

[Antisocialg1t]

I recently replaced our children's phones and sold their old phones. Previous phones were also purchased by me, however DS wanted a better phone so was given the option to put money towards it (approx £100).
I've ebayed the old phones, not unsurprisingly DS's phone sold for more money (approx £75 more).
Should I just pocket the additional money?
Or is DS entitled to some of the extra money?
We're not poor, we don't need the money but also I don't think it's healthy giving them cash on top of a new phone.

Keep the cash, you sold the phone. You bought the new one..

DS wanted a better phone so was given the option to put money towards it (approx £100).

This option was presented and agreed, DS paid. DS also had the option to not contribute and accept the lesser phone- if this had happened, you'd not be questioning giving them proceeds from the sale.

If it’s sold for more because he put £100 towards it, then yes it’s his money! I’m surprised you’re even asking. You’re not “giving him cash” he’s just having part of his initial payment returned to him. Otherwise you’re profiting from his money, which I suspect is a lot for someone of his age.

I would return the money in proportion to I pint so if you covers two thirds and him the £100 was a third he gets a third back

He put money towards that phone in the first place and it sold for more money, so yes it’s his, or atleast some of it.