Greater possibility that William would have arrived in Weymouth (incorp. 1635)during the early 1630's. In 1634 there were at least 20 ships from the ports of Weymouth, Dorset and Plymouth set sail.
Also found details submitted to LDS by a Robert Henry Warren SCADDEN (listed as a relative). This person may have carried out some investigation and found the following:-
William Chard christened 15 May 1625 Thorncombe, near Axminster, DorsetFather: Thomas
Thomas Chard married Johan Pinson 23 Jan 1618 Thorncombe, near Axminster, Dorset
Your William named his first son Thomas and second daughter Joann (a spelling variation). First daughter and second son may have been named after Elizabeth Pratt's parents. So fairly likely they are linked, in fact the details of William's children may have been submitted to LDS by the same person Robert Scadden.
Since he has exact dates above I would say that he has located the original church records or some other historic record. Would be good if you could track down Robert Scadden (if still alive) or one of his descendants.
I hope all of this helps you
Good Luck Peter Chard Australia
Shipping lists may turn up a Thomas Chard and wife Johan and may not list childrens names