In a recent accademic paper (John S Plant (2005) Nomina, 28, pps. 115-133), I have opined that the meaning of the Plant surname is 'offspring' (it means 'children' in Welsh). I have come to this conclusion not least because surnames such a Childs are found close to its early origins.
This does not of course mean that there is a genetic connection between Plant and Childs. However, it is interesting that the DNA evidence shows that Plant is largely a single family even though it is widespread and prolific (so far, 11 out of 16 tested Plants have DNA matched). It is also interesting that the DNA results for the Childs project include a male-line descendant of Henry I Childs, b 1805, Baltimore, MD who matches 11/12 with the Plant Y-DNA signature. This is not an exact 12/12 match and it is not fully conclusive that this Childs has the same male-line ancestry as the Plants but it is a possibility to keep an eye on.
The Plant Y-DNA signature has been established up to the 25 marker level (indeed I have measured my own signature up to 37 markers but there is no other Plant with whom to check that the extra 12 markers beyond 25 match exactly). A fuller account of the Plant Y-DNA results is given at:http://www.plant-fhg.org.uk/dna.html
It would be interesting if the Childs Y-DNA signature could be established up to a larger number of markers as this could help to clinch whether or not Childs and Plant are truly from the same family.
Good luck with your Childs project,
(Co-ordinator of the Plant-like names DNA project)