Pop of colour
To create a pop of colour in your image, look for colours that will contrast with one another. Either through their saturation, brightness, or colour type. Dominant colours will draw the eye first,, but you can create a contrast with other colours too, provided they are sufficiently opposite to what makes the bulk of the background.
An autumnal palette
If you want to emphasize the glorious autumnal palette, aim for most the elements to fit within the same colour family. This means aiming for your kids clothes to either follow the same colour group or be neutrals that will not draw the eye unnecessarily away from the other harmonious tones.
Soft and gentle light
As much as I love the drama or hard light, i really appreciate the gentle beauty of diffused, soft light. A lightly overcast day means I don't have to worry about harsh shadows, blinding my children in the strong light, or worrying about bleaching out the colours. Soft and gentle light lets the colours show their depth, skin tones look better and the whole world takes on a softer look.
TOP TIP : in overcast weather, the colours will look more saturated and warmer if you switch the White Balance in your camera to Cloudy or Shadow setting. It automatically warms up the light, further adding to the autumnal feel.
Hard light can be beautiful
Hard light, when treated well, can be absolutely spectacular. My favourite thing is to use it for back light ( so the light is in front of you but behind your subject). Anything that's slightly translucent will let the light through, emphasizing colour and if the sun is not too high above the horizon, youcan get a brilliant rim light - as if someone literally drew around your subject with a golden sharpie.
Colours like repetition
Colours love to be repeated. Pick a colour that is represented in the scene by something else and the image takes on an extra dimension, guides the viewer's eye better. It doesn;t have to be a big thing - have your child hold a leaf of the same colour as one of the trees in the background or wear a hat that's the colour of their boots - it all helps with how our brains 'read' the image!