Background: Children with familial high risk of schizophrenia (FHR-SZ) or bipolar disorder (FHR-BP) are at increased risk of developing similar disorders and show cognitive deficits during childhood. The aim of this paper is to investigate visual attention and its developmental trajectories in children with FHR-SZ and with FHR-BP to increase our knowledge about potential cognitive endophenotypes of these two disorders. Methods: We compared the performance of 89 children with FHR-SZ (N = 32), FHR-BP (N = 22), and population-based controls (PBC, N = 35) at age 7 to that at age 12 as well as including 133 12-year-old children with FHR-SZ (N = 50), FHR-BP (N = 43) and PBC (N = 40) to investigate visual attention, as part of the Danish High Risk and Resilience Study. We used the TVA-based whole report paradigm, based on the Bundesen's Theory of Visual Attention (TVA) to investigate visual attention. Results: Children with FHR-SZ that showed deficits in visual processing speed at age 7 improved to a level that was not significantly different from controls at age 12. All children improved over time. We found no attentional deficits in FHR children at age 12. Conclusions: On visual attention, children with FHR-SZ did not show developmental deficits or lags and, together with children with FHR-BP, they develop similarly to control children between age 7 to age 12. This emphasizes the potential of beneficial neuroplastic changes in cognitive deficits found at younger ages in children with FHR-SZ. It also highlights the importance of identifying and characterizing cognitive developmental trajectories of high-risk children and provides hope that visual attention may develop appropriately in these groups.