@katrina2017 Giving a present to the other children is a sticking plaster, it's not solving the root problem.
You're better off helping the child to learn that, firstly, it's okay to sometimes be disappointed, but that disappointment doesn't need to ruin the rest of their day, and secondly, try to reframe that disappointment for themselves as happiness for the other child - try to see the positives, etc.
And, yeah, on the day of a birthday party is not the best time to be handling it but there's lots of opportunities for learning these things at other times so, when it comes to the party, it's something they've dealt with before but maybe a slightly more challenging version of it.