My daughter was a babe in arms when I took her to City's penultimate game at HR (I entered fatherhood late and have added since!)
She'll have no memory of course, but I wanted to take her just in case she turned out to follow City. She also went to the first game at Ricoh a few months later. My reasoning was that it would be something of a 'momento' for her. She attended, with me and the now ex for a handful of games after, but there was a long gap until she went again when I took my then 13 month old boy to the Bristol City home fixture last season. Again, he will have no recollection, but he did have his pic taken with both Oggy and Sky Blue Sam. There is a little more serious intention attached with taking my boy - I now live in Sutton Coldfield, and he was born (takes a gulp) a Brummie.
It's a bit of a blow in all honesty Brian, but nothing a bit of tippex on a birth certificate can't sort out. Given our location, he's gonna have his head turned as he becomes familiar with footer. I can see a potentially traumatic time ahead for me but I promise to fulfil my duty.
I didn't attend my first game until I was almost 9 y o. I've jokingly ribbed my Dad over the years that I should have been taken younger (even tho it was his final season with us, I never saw Bill Glazier in goal)
Kids react differently to their first match outings, but I would definitely take your 4 y o. Based on my own 'late' first attendance, she will only thank you in years to come, Surely?