I think Ricky probably hit the nail on the head - it was cheaper to have them done as a "job lot"! 
Bill
Under Ecclesiastical law no fee can be charged for the administration of Sacraments. “Sacramenta sunt libere conferenda” is the rule prescribed by Pope Innocent III at the Lateran Council and contained in the Decretals of Gregory IX. This rule is emphasized by the canon of Archbishop Stephen Langton made at the Council of Oxford in 1222, though the canon suggests that a fee may be payable where there is an ancient custom to that effect.
One nineteenth century Bishop said that to charge such a fee was “downright and glaring simony.”
The Baptismal Fees Abolition Act was passed in 1872, under which no fee can be charged for baptism notwithstanding any ancient custom to the contrary.
The purpose of this act was to make the law clear in respect of fees for baptisms or for registering baptisms, it appeared that fees were being charged in some parishes, and it was intended to put an end to this system.
In one case where a rector demanded a fee of two shillings for a baptism legal opinion was that;
a) No fee can be claimed for the registration of a baptism;
b) It is very doubtful whether in any case, even where there has been a custom to do so, a fee can be asked for the administration of baptism;
c) It is certain that no such fee can be recovered by law;
d) It is also certain that any clergyman refusing to baptize or to register the baptism on the ground of no fee having been paid can be proceeded against and punished under the 68th and 70th Canons of the Act of 52 George III., cap. 146.
Stan