Local libraries often have story times and activities (like music or art classes) for young children and their parents. Ask about it next time you're there to find out dates and times of the activities your library offers.
These are often great ways for both you and your little ones to make new friends.
Before you leave, pick out some books together to read at home.
Summer isn't the only time of year you can get outside. When it's cold and snowy, go out and build a snowman together.
Just be sure to bundle up. But, don't be surprised if your toddler gets tired of all the layers quickly and wants to head back inside; that's totally normal. Just follow it up with a snack and some yummy hot cocoa.
This could be with other family members, church friends or your newfound library story time friends. Make time occasionally to get together with other moms and kids for play dates. This could include going to each other's homes, or going to any of the places or activities mentioned above together.
It doesn't matter how young your child is; the social aspect of play dates is as much for you as it is for them.
And don't be afraid to reach out to others and invite them along. It's likely they are looking for activities like these as well.
Visiting a family member, like a grandparent you don't see often enough, is also a good way to spend a day when you're feeling lonely. Maybe they are as well.
Days inside with nothing to do (but so much to do) don't have to become the norm. Even if it takes stepping outside of your comfort zone, give a few of these things a try. You may just end up being really glad you did.
Also, check out this article for some really great, creative (and easy) toddler activities.