On sunny days have kids move to shade. The subdued light is flattering to people and will help prevent squinting. Consider taking pictures later in the day . The soft golden light just before sunset can be beautiful and give a glow to the photograph. Take lots of pictures of the same thing .
Professionals take dozens of shots to get one great one.
Kids do splash in bathtubs, do blow out birthday candles, do sit in their highchairs covered with food. That's the fun of childhood. Shoot both candid and posed . Candid isn't better, just different. Don't nag kids to pose .