Robert and his wife Eleanor did not have any children.
There is a note in Robert's overview - "dvp, dsp. Died during the lifetime of his father without issue"
Two reliable sources I trust, Magna Carta Ancestry, 2nd Edition & genealogics.org do not record any children for this couple.
Have removed Catherine De Ufford as a daughter.
Here is conclusive proof that Robert and his wife Eleanor died "without heir of their bodies" before his father.
"the said feoffees, by fine, granted the manors to Robert de Ufford, son of the said earl William, and Eleanor daughter of Richard son of Richard late earl of Arundel, in tail, with reversion to the grantors, and Robert and Eleanor died without heir of their bodies, and William, the earl, then entered into the manors"
Date: Westminster, 20 July 1376
Source: Calendar of Patent Rolls Vol. 16, p. 299
http://sdrc.lib.uiowa.edu/patentrolls/e3v16/body/Edward3vol16page02...
I will add this page as a source.