If there are K kids, they each eat 6K strawberries. There are 7-K adults, who each eat 10(7-K) strawberries.
Together they eat 68 strawberries, so 6K+10(7-K)=68, 6K+70-10K=68, 2=4K, so K=½!
So there’s something wrong with the question!
My guess is that they ate 58 strawberries, so 6K+10(7-K)=58, 6K+70-10K=58, 12=4K, K=3. There would be 3 kids.