We have carried out a deep, 3.6 cm radio continuum survey of young outflow sources using the Very Large Array in its A configuration providing subarcsecond resolution. The eight regions observed are Haro 6-10 and L1527 IRS in Taurus, Haro 5a/6a in OMC 2/3, NGC 2023 MMS, NGC 2264 IRS1, HH 108 IRAS/MMS in Serpens, L1228, and L1251A. In combination with our similar and previously published maps of eight other star-forming regions, we find only one region with a single source, while the other 15 regions have on average 3.9 nearby sources. This supports the view that isolated star formation is rare. We have selected 21 objects, which are all young mostly Class I sources, and find a binary frequency of 33% in the separation range from 0.5" to 12". This is within the uncertainties comparable to the observed binary frequency among T Tauri stars in a similar separation range. Seven of the 21 sources drive giant Herbig-Haro flows. Four of these seven are known to have companions (three are triple systems), corresponding to 57%. We discuss these results in relation to the hypothesis that giant Herbig-Haro flows are driven by disintegrating multiple systems.