I love my time with Josh (3) and Sam (9 months), but I miss talking with the people at work and using my mind in a different way. I don't really want to get a job, I just want some kind of change at home.

You're bringing up a widespread and complex issue, and here's a brief summary of suggestions:
Cultivate community, especially with mothers. That will reduce monotony, give you emotional support and a helping hand, and satisfy the tug in your heart for the company of other mothers.

Leave your work-mind behind. You just can't do motherhood like a day at work. The same pace will frazzle your nerves.
Use your work skills. On the other hand, there's no sense in forgetting the work skills you've got that could be useful at home, like helping organize events for a mothers club or preschool.

Take it easy and enjoy this time. Some women feel guilty about savoring the wonderful moments at home. But you're entitled to! Each day, you handle situations that are harder than most work problems, so when you get an opportunity to relax, grab it and linger. You don't have to keep the house spotless in order to justify your (supposed) "vacation" as a homemaker: it's not a vacation, as anyone well knows who has taken care of young kids all day. You've earned this time with your children, and it won't last forever. Plus you absolutely need to rest whenever you actually get the chance, in order to settle down the stress chemistry in your body and nurture your health and well-being.

Feed your mind. Many mothers pursue a natural subject: child development, health, and family relationships. You could return to an interest you had before children, such as playing a musical instrument, writing letters to help free political prisoners, etc. Or take up a new interest. You could also stay current in your field, so that reentry to work goes well.

Manage the boredom. Taking care of children is often amazingly BORING. Paradoxically, what works is to pay closer attention, noticing details you'd normally overlook. This makes an activity more interesting and draws you into a peaceful awareness. Also, look for the nice parts in your activities, or nudge them in a more enjoyable direction.

Find respites. Every day, you need relief from interacting with your child, such as your partner giving her a bath while you watch TV, another mom coming over with a child who plays with your own, or formal childcare. Study what drags the needle on your internal stress meter into the Red Zone, like four hours in a row alone with an oppositional three-year-old, and do everything in your power to change those things so you never "redline" with stress.

Nurture your sense of worth. Staying home means finding new sources of self-esteem. The first place to look, of course, is your role as a mother: it's the plain truth that you are making a great contribution to your children, and the honor legitimately due you for that is magnified by any sacrifices you've made to be a mother. Next, you could get involved in your children's activities or other kinds of community service, giving you a greater sense of making a difference in the world.

Finally, try to use important abilities within yourself. For example, if you enjoyed using your analytical intelligence at work - perhaps you were a CPA or computer programmer - you could read fascinating but challenging books such as A Brief History of Time. If you worked in TV, try volunteering with community access television. If you liked public speaking, consider joining Toastmasters.

Check in with yourself - Keep paying attention to how it's really going for you. If you try some of the suggestions above and you still feel something important is missing, it could be a sign that you need to shift gears, perhaps by returning to or increasing your work.