Hello Jo
Didn't they tend in those days wait for a while, even until another child came along before they had them baptised. The fact the grandfather was a school master in Cwm may have been influential in having the children baptised. Its just thoughts. The fact David was baptised the day of his twins funeral probably for that reason. Also it crossed my mind had Thomas not been baptised then they would have included him too. He was 4 yrs old by then.
regards
tisgrannie