Children that are learning to speak two languages should reach the same developmental milestones as children that are only learning one language. These milestones would include one word by age one and also able to use two-word phrases by age two. However, it is common for children that are exposed to more than one language to mix up grammar and syntax rules.
If a child has been acquiring one language, and then another language is introduced, there may be a “silent period” for several months while they are learning the second language.
So, does speaking more than one language cause a speech and language delay? There is no evidence that speaking more than one language causes delays.