Golf Grip and Stance Basics for Junior Golfers

The two fundamentals worth getting right before anything else - how a child holds the club and how they stand to the ball.
Grip: the ten-finger (baseball) grip is fine to start
Most golf instruction eventually moves a child toward an overlap or interlock grip, but there's no rush. For very young beginners, a simple ten-finger grip - where all fingers of both hands wrap around the club, baseball-bat style - is easier to control and perfectly fine while a child is still building basic hand strength and coordination. The interlock or overlap grip can come later, once a child has some reps in and a coach or parent can check it properly.
Whichever grip is used, the same basic checks apply: the club should sit more in the fingers than deep in the palm, and grip pressure should be light - imagine holding a tube of toothpaste without squeezing any out. A grip that's too tight is one of the most common causes of a tense, restricted swing in young golfers.
Stance: shoulder-width, athletic, and repeatable
A good junior stance doesn't need to be complicated. Feet roughly shoulder-width apart, weight balanced on the middle of the feet (not the heels or toes), knees softly bent, and a slight forward bend from the hips rather than the waist - the same athletic-ready position you'd see before shooting a basketball free throw or fielding a ground ball.
The most useful thing a parent can do without technical golf knowledge is check for consistency: does the setup look roughly the same before every shot? Kids often rush the setup when they're excited to swing, and a rushed setup is a common source of inconsistent contact - well before swing mechanics become the issue.