A T-ball glove for 4, 5 and 6 year olds is 8.5" to 10" at every position on Rawlings' chart; Baseball Monkey puts under-7 infielders at 8–10.5". Start at 9" for a 4-year-old and 10" at 6. A small glove the child can close beats one to grow into.
Two charts at 4–6
Rawlings lists t-ball (3–6), all positions at 8.5–10"; Baseball Monkey’s baseball, ages under 7 band gives 8–10.5". They overlap at 8.5–10", and the sizer picks the middle: 9.5".
At 4–6 a pitcher’s glove (9.5") wants a closed or basket web, a middle infield (2b / ss) glove of 9.5" an I-Web, and a third baseman’s 9.5" an H-web.
The game at 4–6
In Little League a 4–6-year-old plays in Tee Ball (ages 4–7); Minor League (ages 5–12, 46 ft pitching, 60 ft bases). The next step is Little League (Majors) from 9.
CDC growth charts put the median 5½-year-old boy at 112.4 cm (3'8") and girl at 111.5 cm (3'8"); the 5th to 95th percentile for boys runs 3'5" to 3'11". A tall player at the age is often a size ahead in the hand too.
Check the hand
Adult hands vary more than any chart: measure it 1:1 in Mode 01 and the sizer moves the pick toward the top of the range for a long hand.
For comparison, the next sheet starts from 9.5".