private WhatEverClassThisMayBe _TheOneAndOnlyChild;
public|private void showChild() {
if (this._TheOneAndOnlyChild != null) {
this._TheOneAndOnlyChild.Close();
}
this._TheOneAndOnlyChild = new WhatEverClassThisMayBe();
this._TheOneAndOnlyChild.Show();
}
Something like that, would be my guess...