Find Ancestors

hello to all you people out there,i,m trying to find my neice and nephew,claire louise brown and andrew steven brown,they were born in england lived at 16,cornleaze withywood bristol for a bit then moved to bridgend in whales due to there fathers job promotion,there fathers name is steven henry brown there mothers name eva burns they came to visit us a couple of times then next thing we new steven went to work one day on his return a letter was waiting for him on the shelf to say eva had taken there 2 children to londonderry belfast to start a new life with her family what already lived there(she planned it for weeks behind stevens back)he had contact a while after steven and there nan(joyce brown)and granfer(henry brown i.e harry)sent parels of clothes to them a couple of times but never got any replys from then on its as if they dissapeared into thin air eva cut of all comunication to the childrens family all of us has been heart broken ever since there is not a day goes past we dont think of them we have there original birth certificates thats one thing eva did not take i suppose she had her reasons but it was a very cruel thing to do we doted n those kids claire was the eldest grandchild there date of births are 29/07/1979 claire and 28/11/1980 andrew of coarse i bet they may have differant surnames now but only by depol or claire maybe married now..the brown family came from dunster road knowle bristol and still live there have done since september 1958 so there is no excuse there for contact...anyway i hope there is someone out there who reads this message and knows some imformation as to there whereabouts we have photos if needed and can not wait to hear from them missed and loved very very much..thanks to everyone..fingers crossed