Amac1:
I simply want to know have I been sinning by not taking them in the past?
No. My parents would not take me to Mass until I was old enough to sit quietly in the pew for the whole time. My earliest memories of being at Mass are around age 4 or maybe just slightly younger.
My mother strongly believed that babies should not be at Mass until they were old enough to behave, unless there was a suitable “cry room”, which our parish church didn’t have. So on Sunday, she and Dad would attend separate Masses, and the one not at Mass would stay home with me. I realize some parents like to bring their small children to Mass or may not have a reliable sitter, but I am just pointing out that it’s not a sin to make other arrangements for your pre-school child rather than take them to Mass.