If my s/o has juvenile diabetes, how likely is it for our kid to get it?

“In general, if you are a man with type 1 diabetes, the odds of your child getting diabetes are 1 in 17. If you are a woman with type 1 diabetes and your child was born before you were 25, your child’s risk is 1 in 25; if your child was born after you turned 25, your child’s risk is 1 in 100.” (Source about halfway down the page.) There are some other factors in the role of genetics discussed there as well. Hope that helps some.

The development of Type I diabetes is a result of the interaction of environmental factors with ten or more distinct genes. It is difficult to predict the inheritance in such a multi-gene, multi-factor situation. What applies to millions of people see @Seaofclouds answer does not apply well to any one person or couple. It comes down to wait and see and be prepared to recognize the signs of its occurrence even in an infant or young child.

I’m not all up on diabetes but, apart from genetics, lifestyle does play a part on whether someone is born with diabetes (or gets it later in life). Perhaps you should be looking at your own lifestyle and ensure that you don’t smoke, drink alcohol or caffeine in excess, and many other things that I’m sure that you are aware, just to be on the safe side and to improve the chances of a good birth.