A yellow diamond sign with two children walking means:

Two children walking on a yellow diamond is the school zone or school crossing warning. It alerts drivers to an area where children are likely to be crossing or walking near the road. Reduce speed, prepare to stop, and watch carefully — children are unpredictable. Many states have specific school zone speed limits (often 15-25 mph) in effect during certain hours, marked by additional signs or flashing lights. Penalties for speeding in school zones are typically doubled. Even outside posted school hours, the warning sign is in effect because the road geometry that makes children's crossings dangerous does not change. Pedestrian crossings (one adult figure) and playground areas have separate signs.