Being English do not know what first grade is but it sounds as though it is probably similar to the various stages in our national curriculum so would that be something like 5 - 7 age group?
You are certainly one proud grandpa, I think it is great that children learn computers early it make them unafraid of the technology and so much more confident later when they will have to use them. A friend of mine who I went out for a meal with earlier this week was telling us all that her 5 year at school one of their recent lessons was to take a digital photo, connect the camera to the PC and print the picture out. As they have a PC and digital camera at home he virtually did it all on his own and saw nothing in it which was a contrast to a couple of others in the group who said they would not know where to begin with that task. There are obviously dangers in children using computers intensively at an early age but IMHO if channeled correctly and balanced with other activities I think it is great and can only assist they long term development and opportunities in life.
As much as I am sure your daughter loves to bring them over to you to look after I bet you love it more LOL. Its great you have the opportunity to enjoy them young and see them grow up, God Bless you and sustain you in assisting to be a positive male influence in their lives.
Here's the BSAEC* for my area.
Kindergarten: must be five years old by a date somewhere around September 30 to enroll
1st grade: 6-7
2nd: 7-8
3rd: 8-9
4th: 9-10
5th: 10-11
6th: 11-12
7th: 12-13
8th: 13-14
9th: 14-15
10th: 15-16
11th: 16-17
12th: 17-18 at which time the graduate is seven times smarter than all his elders combined
Some elementary schools end with the fifth grade; others at sixth grade. Next level is usually called middle school, at least on the Left Coast (used to be junior high). The final third is for high school.
*Basic School Age Enrollment Chart