Hello and welcome to the forum, we love having new people on here, who ask questions. You are obviously over the moon with your beautiful pup, dogs are a real pleasure to have around.
Boxers are beautiful dogs, but not the fastest to mature, as I'm sure you've already noticed. At 13 month she is still a pup, both mentally and physically, and although she is old enough to get pregnant and give birth, it is probably not that good for her at this moment in time. As she is still growing the pups will take the nourishment she needs herself to reach maturity.
You should be thinking in terms of another year, you could use this time to do some investigations to ensure you are doing the best for your girl. I am not familiar enough with the breed to advise you on any health tests that need to be done on your pup and the dog you would like to use as stud. There is lots of information on the kennel club website, you may have to travel to get some of the test done, but well worth it to ensure a healthy litter.
You could also speak to other boxer breeders to ensure there is a demand for the breed, pups can be fun, but are hard work if you still have them at six months.
You say in your post you have children, you must be a very busy lady, a litter of pups can be time consuming, so you also need to think about if it is right for you. They can also wreck your house, a friend of mine bred a litter of labs, one of which we had for 14 years, he was a wonderful dog, but I think the breeder is still getting over the experience, she never had another litter, she decided buying one was easier.
Hope this helps, I'm sure you will get lots of other nice replies.