Children's Intelligence Tests Pose Challenges for MLLMs? KidGym: A 2D Grid-Based Reasoning Benchmark for MLLMs. - Hengwei Ye; Yuanting Guan; Yuxuan Ge; Tianying Zhu; Zhenhan Guan; Yijia Zhong; Yijing Zhang; Han Zhang; Yingna Wu; Zheng Tian (CoRR, 2026)