I would want to clarify few things for you.
You were not suffering from any thyroid disorder
during your first pregnancy
because your hypothyroidism
was caused by post partum thyroiditis
which occurs after many weeks of delivery of the child.
Other thing is that a person suffering from diabetes type one has more chances of developing autoimmune thyroid disorder and not the vice versa.
As far as development of type 1 diabetes
in your child is concerned,the exact cause of type 1 diabetes is unknown. Scientists do know that in most people with type 1 diabetes, the body's own immune system — which normally fights harmful bacteria and viruses — mistakenly destroys the insulin-producing (islet) cells in the pancreas. Genetics may play a role in this process, and exposure to certain viruses may trigger the disease.
Make sure that you are not hypothyroid any more as any hypothyroidism,at the moment,would harm the growth of your second child.