The children's powers might be more focused on restoration rather than destruction. Given that they are a new generation, they could have powers that are the opposite of Thanos' in some ways. So while Thanos was all about obtaining the Infinity Stones for destruction and control, his children could have powers related to using the energy of the stones in a positive way, like healing entire planets or restoring lost civilizations.
Percy's powers are based on water and his demigod abilities. Thanos has the power of the Infinity Stones. If they were to interact, Percy's water could potentially disrupt Thanos' use of the Power Stone's energy blasts. For example, water could absorb or deflect the energy.
His powers could be a mix of ninja skills and Thanos - like abilities. He might have enhanced physical strength similar to Thanos. His Rasengan could potentially be charged with some sort of energy related to the Infinity Stones. Also, his ability to sense chakra might be modified to sense other forms of power. Maybe he could even teleport like Thanos does in the comics, which would give him a huge advantage in combat.
It could be the main protagonist if the story is written in a way that the character manages to control and utilize all the Akatsuki powers effectively. With the combined powers, they would have a vast array of abilities at their disposal, making them extremely formidable.