Hello L23,
In the 1851 census index for Muirkirk, Ayr, is the family below.
Beck Robert, age 38y,
Beck Jean, age 40y,
Beck William, age 12y,
Beck James, age 10y,
Beck Robert, age 8y,
Beck Agnes, age 5y,
Beck Janet, age 1y.
Its not unusual for two children of different ages from the same family to be baptized in Scotland.
Regards,
Jonn