Fathers Stomach cancer. An early stage?

So my dad recently diagnosed stomach cancer at age 68. My dad just complained about stomach pain last two months. It was stage 4. He was fit and fine. Nobody could tell. his ultrasound looked good, just showed retrolymph nodes enlarged. Blood reports also were good. They got to know from endoscopy. Then a Biopsy. His all brothers were drinking lot being in village and poor we dont know exactly how they died they too died in may b 60s or 70s. We thought they died due to drinking. So i dnt know if they had cancer. As they were poor and nobody went to hospital much. Now i have seen few cases were if family had stomach cancer their children too having. So just for precautionary measures to detect early cancer. I want to know what kind off test i can do every year for me. I have a toddler whom i want to test and keep observing in future. Please suggest what test can determine any type of cancer?? How to detect at an early stage??? I want to know about test, every year to b safe