To capture such happy moments is a great idea, because it is a less formal setting, and the beauty of nature brings out the best in you. This is the real essence of your photograph; the person you are yourself, and the wonderful person your family makes you. Here are some tips on capturing the most beautiful outdoor family portraits.
A photographer will also be able to give you ideas about the location, what to wear, how to pose, while accommodating your suggestions and keeping your comfort in mind. Find such a professional who is well versed with family portrait photography, and who knows what she/he is doing.
Whether it is in your backyard, by the beach, at the countryside, or in a forest, choose a location that you are most comfortable with. Usually, locations that exude the vibrancy of nature are the best choices.
You may also choose to have pictures clicked with monuments in the backdrop. However, don't choose ruins of old buildings (unless you are the Adam's family), or a commercial building as a backdrop. These locations are more suitable for individual photographs. Try to come up with some creative ideas in terms of the location of the photograph.
What to Wear
The beauty of outdoor family photography is that it allows you to dress comfortably and less formally than a photograph clicked indoors or in a studio. You can wear bright colors with prints, but ensure that your entire family is coordinated within a color scheme.
However, you should wear clothes that you are comfortable in, and clothes that are your style. Don't wear clashing colors or very bold prints, otherwise the essence of the photograph will be lost. While your concern about what to wear is absolutely valid, just remember that comfort is the key to a good photograph.
Since this photography is less formal, the way you pose is entirely up to you. It is a personal belief that outdoor pictures should be more spontaneous than pre-decided. Capturing a family member in her/his true element will make the picture more perfect.
With inputs from your photographer, you are sure to come up with some great poses, and eventually, a gorgeous photograph.
These ideas will materialize based on your perception and what exactly you want from the picture. One of the most important tips is that since it is something you are doing particularly for yourself, ensure that you do what you think brings out the best in you. This will make it perfect and very special for all of you.