Many divorced parents spend more time with their kids in the summer than during the school year -- particularly if they live some distance away and/or don't have primary custody of them. If you have a new significant other in your life, it may be difficult to keep that relationship from them -- and you may not want to. You love this person, and you're sure your kids will, too.
However, it's essential to go slowly when introducing your kids to your new partner. Talk to your co-parent first. It's typically not a good idea if they learn about this person from your children rather than you. Your co-parent may have some thoughts (or requirements) regarding how much this person can be around the kids and under what circumstances.
Some parents include rules about significant others in their parenting plans. This can make expectations clear for both parents. If you didn't do that, this may be a good time to establish some rules -- even if you don't codify them yet.
Once you get your co-parent's approval (or at least acceptance), it's best to start talking to your kids about this new person before they meet. If they're old enough, give them some input into what they'd like to do together. Would they like your new friend to join you for dinner at your favorite pizza place or for a picnic in the park?
It's often best to keep these initial visits short and somewhere other than your home. As your kids grow to like and trust this person, you can consider a day at Six Flags or maybe a game night at your house.
Let your children feel comfortable telling you how they feel. Don't expect them to accept your new significant other right away. They may have a difficult time seeing either parent with a new partner.
As your significant other becomes a more integral presence in your kids' lives, it may be wise to include some expectations for things they can and cannot do -- for example, actions surrounding discipline -- in your parenting plan. While you may bristle at this if your co-parent suggests it, remember that they'll apply to people with whom they become involved as well. Your family law attorney can help you as you work out these modifications to your parenting plan.