Hi Claire,
A preliminary search proved very easy.
A quick guide to the procedure of the orphans' court: if a freeman of the city of London dies with children under 21, the executor/administrator (often the widow) is bound by a recognizance to provide an inventory of the estate. Once the inventory is approved, the executor is bound by another recognizance to set aside a third value of the estate for the orphans. Once done, the court determined custody of the orphans. Subsequently, interest from the third portion could be used by the guardian to pay for costs, particularly education, of the orphans. When they are 21, orphans return to the court and sign off receipt of their portions.
For Elizabeth Curson the process begins on 17 Nov 1603 (this is in the Court of Aldermen Repertories). The inventory is approved and on 14 Mar 1603/4 she sets aside a third portion (100li) with four sureties:
herself,
Humphry Rosser, armourer,
George Hickson, skinner,
William Carpenter, skinner.
('armourer' and 'skinner' typically indicate company membership)
They are bound to secure the money with a penalty of 120li. This is quite low, suggesting they were deemed highly trustworthy by the court. For some reason, presumably clerical error, Leonard is described in the repertories as a citizen and draper (pannor[ius]).
There is a copy of the bond in the Letter Books, which has signatures from the sureties -- including Elizabeth. This also correctly describes Leonard as a weaver (textor[ius]).
If you are interested the LMA ref. for this is COL/AD/01/027, f. 183. Letter Book BB.
I recommend tracking down info on the sureties, and definitely read their wills if they left any. Orphan sureties are quite often friends or relatives of the bereaved family.
Note that there will be more information in the court, possibly details of the orphan's upbringing, but finding them will require a substantial search. Check back with me in a year or two and I may have more!
Something I spotted by chance: there's an entry in the repertories 14 Dec 1603 ordering that Elizabeth Curson, widow, may sell seacoals provided for the poor by retail at five pence the bushel.
I recommend checking the LMA and National Archives catalogues for Leonard as there are promising looking property and legal records that may take you back further.
all the best,
Mike