The following portions of this answer are aimed at helping mom get some social time too(this helps to set a good example, plus even homebody's such as myself need time away from time to time anyway):
You might try determining a night or two each month for her to endeavor in an area she would like to "try." She has her career in hand, but has there ever been a hobby she'd like to try but never got around to? or an avocation she'd love to take a class about? Maybe she'd like a book club. This kind of activity will get her out of the house and away from the tedium of small children (something everyone needs) AND might offer her the opportunity to meet some new people with similar interests (she'd have to get out of her comfort zone and introduce herself and chat a little for this second advantage though). For these kinds of activities, the local library and community college or university are good places to start.
Along the same lines, if she is athletic, the YMCA or parks and recreation organization in you area msy offer adult team-sport leagues she could become involved in. Of course, there are also various "club sports" in different locales.
Now for ideas that might help mom and kids
Many mother's join "mom's groups" or "play groups" and meet once a month with other stay-at-home mom's. Its a chance for all the kids to interact and the mom's to network and socialize with other mom's. A site like mommeetmom.com or meetup.com (specifically here) might be helpful if that looks interesting to your wife.
"mommy and me" classes are a good way to meet other moms and their kids (and create some early kid socialization and friendships with moms of kids of the same age as yours - this might lead to cool friendships for the kids later on).
Is there a place she and the toddler can take a class while the baby is cared for that would be of interest to them both? Again, athletic activities like swimming are offered at the YMCA. Some private schools also have such programs in the after-school hours as additional income for the school and I've known of boutique baby stores that offer such classes at the store site as well - a simple search online for your area should yield something.
Ideas for the Kids:
Get the kids involved (as soon as they are old enough) in interest-area classes at least once/week. Parks and Rec in our area offers some crafts lessons, but of course there are ballet and tap classes, various sports to try, and any number of other kinds of activities - again depending on the specifics of your location.
Throughout the summers our library offers far more than storytime with puppet theaters and magicians coming in once/week for special summer programs - Even Home Depot offers occasional classes for kids.
Lastly, at age 2 and younger, most kids really only engage in parallel play anyway so specific socialization with other kids of the same age doesn't begin in earnest for kids until about age three or four when they begin to develop the ability to "pretend" and starting actually playing with, instead of next to, others. For this reason, I encourage you not to stress over the matter too much, but keep it mind and also know that any outing (even to the grocery store) as well as moments they have about learning "manners" interacting with you and other family members and especially in relation to relating to and empathizing with one another are also moments when they are learning social skills. Especially as they move into ages three and four, the more you can sit down together to eat dinner together, the better off they will be even if it is just the four of you in terms of many social skills and in building a conversive relationship with you - the most important people in their socialization - mom and dad.