Bring them! If your newborn will have loving older siblings they should absolutely be included in the maternity and newborn pictures! I wouldn’t suggest that you have them stay for the entire session though. As a mama of two, I know that kids can get bored and antsy.
If you are lucky enough to have family in town, have them come along to help take care of them during your session, and then take them somewhere fun after their part is done. If your family isn’t in town, bring a friend.
We can take some pictures of you by yourself first, so your kids can see what I am doing and get to know me some, then we can get some pictures of you with your kids, and end with adding your husband in for some whole family pictures before sending your kids on their way.
Sometimes it helps if the kids know there is a special treat (ice cream, a trip to the playground, etc.) waiting for them if they do a good job.
Also, make sure you arrive to the location in the outfit you want to wear during your family portion of the session, so your kids don’t have to wait on you to change. Once they head off for fun with family or friends, then there will be plenty of time to focus on you and your husband (and your baby if it’s a newborn session)!