MDI Child form problem....

Question

hi forum, i have created mdi parent & child form. when i click menu option to open child form it opens. now i kept it open and again i click menu option & i got new instance of form. ( another same form i got ) what to do to stop this problem ?? i m really confuse. using flag it is done. but other simple way ????? please guide me thank u, bhavin gajjar