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By 21/2 yr a child should usually speak in a sentence, able to follow commands and may sing a poem.
If your child is just speaking bi syllables then he has a mild speech delay
.you can try to encourage him to speak to other kids while playing or better, send him to playgroup, since sometimes kids learn best with other kids.If persistent this problem requires consultation with a speech therapist or atleast initial consultation with your pediatrician
Hope I have answered your query.