Bear in mind that adults' ages in 1841 were supposed to be rounded down to the nearest 5 years. So an age of 50, if accurate, means a DoB between 1786 and 1791.
An age of 64 in 1846, if accurate, means a DoB in 1791 or 1792, and an age of 59 in 1850, if accurate, means a DoB in 1790 or 1791.
If they were very poor, the parish would have borne the cost, for example, of funerals. It is far more lkely that, for whatever reason, they did not have their children's baptisms recorded in the Church of Scotland's parish register.
Maybe they belonged to some breakaway church or sect whose records, if any, have not survived. Maybe they just never got round to having the children baptised? Maybe the clerk forgot to write them down?
It is possible that there might be something in the records of Carluke Kirk Session that might shed some light on them. The KS records are only available in the Historical Search Room in Edinburgh and one or two other local archives at present, but there are plans to put them online at Scotland's People.