Here's an idea.
Get your children's shoes on and take them all into the back yard. Grab a notebook and pen on the way out. Then, start making a list of the things you see. Are there trees? Birds? Flowers? Clouds? Bugs? In a minute, your children will be running around, calling you to see the Queen Anne's Lace all closed up and gone to seed, bringing you yarrow and hawkweed, finding a deserted funnel web in the grass. Write it all down in a list. Add date, time, and weather. Decorate if you want.
A nature journal does not have to be complicated. It does not have to be perfect. In fact, as I've begun to do it more and more, I've found that the process is more important than the product. It's in the process that you realize how little you know, that you begin to notice and compare details, that you begin to gain skill in capturing what you see, hear, touch, and smell. A nature journal is a record of a learning process.
Anyone can make a list. One list every month can be a valuable record as you notice the changes from month to month. (So many flowers have gone to seed since last month!) A list could be a first step to recognizing what you want to learn more about. (What is that small aster-like flower with white petals and tiny purple flowers in the center?) A list requires no artistic skills. If you keep making lists like this, though, you may find yourself recording --and illustrating-- details of things you want to find out more about.
Keeping a nature journal does not have to be any more complicated than this. If it grows into more, well, you can take that as it comes! You do not have to start out knowing how to draw, or paint with watercolours, or knowing the names of everything you see. Start where you are. Make a list. Discover things to wonder at, things to find out more about. That's all you need to get started.
The joy you find as a parent in nature study and nature journalling will be naturally contagious to your children. I'll be honest, SA(7) still does not enjoy writing or drawing, as that's a natural weak area for him. But I've noticed that when he has gotten out his nature journal, it has been because I was making an entry in my own. All the children enjoyed helping me make this entry in my nature journal. They not only found things for me to add to my list, but they described some of them in great detail. This makes me happy, and I know it has great benefits for them, too.
Don't be intimidated by nature journaling. Make a list!