I didn't want it to go to waste
Stop and think about this idea for a minute. How is it "going to waste" if you simply throw it out?
There is no obligation on the part of the universe for every calorie to be consumed.
All food ends up in the waste system anyway--either as flat-out garbage or as sewage.
OK, OK, some of it ends up in our bodies as "calories consumed." But the only time you need to worry about waste is if you will have to *pay for* new calories to replace the ones you tossed in the garbage.
Food is not in charge.
Food does not decide whehteh it was been "wasted."
Neither to OTHER people decide whether you have "wasted" food.
Only YOU can decide wether you have wasted the food, and that's because only you know whether those calories will need to be replaced.
(that said, I think this was a nice "i'm sorry/poor kid!" gesture, and that your son won't really think he was being rewarded for his tantrum. I don't know how old your kid is, but I feel so sorry for him, having just woken up. I really don't think this ice cream is going to reinforce bad behavior,and it may just make him feel a little better about the whole thing. Like somebody loves him.)