MY YOUNG SON HAS GROWN SWEETCORN IN GREENHOUSE

The male flower if the one at the top of the plant and females usually form in the leaf joints lower down as small tufts. They should usually be produced at the same time and its probably down to natural things affecting them. Sweetcorn prefer to be in blocks outside as they are wind pollinated. If the green house air is still then even if you do get femlae flowers, they may not get pollinated