This is a brief discussion addressed to Ranya Morsi in particular and to linguistic community in general. There is an amazing correlation between the acquisition of tense/ subject-verb agreement in language impaired children and normal children. I find it very interesting and useful to shed light on the topic. It seems that most verbal constructions, if not all, look like imperatives in language acquisition and language impairment.
Based on research on the acquisition of Moroccan Arabic, I found that verbal constructions in 2-3 year-old children lack tense because of the absence of the negative particle at this age. Once the negative form is triggered around 3 years, the tense feature is also acquired. For me there is a mysterious reason why, for children in language acquisition/ language impairment, tense is lacking and/or delayed respectively.