Suddenly backtracks on development milestones
All parents remember those big milestones: their child's first steps, first words, first sentences, first time they said "I love you," and the list goes on. There is a certain level of pride and joy associated with each milestone, as well as an excitement for the next one to come; however, in certain circumstances, the child could move backward instead of forward.
As anyone would imagine, this is scary and disheartening for a parent. If you see that they stop speaking in the manner they could previously, you should consult a doctor. It is likely a sign that the child has autism, and is reverting back to the stage before they began to speak. While it is possible to get the child to begin speaking at the same rate again, it is a very difficult process, and should be addressed only with experts in the field. Don't worry, you and your child will get through it!