I would think you can buy the lightest that is made at 7U which is probably -13 or -14. They don't impose drop limits until they get older in most leagues and I would assume Dizzy Dean is the same.
From the 2009 Dizzy Dean rule book, the only rule regarding bats is found in Section 2:00 Equipment, 2:07 The bat shall be a regulation baseball bat (not softball) (unaltered) made of either wood or an approved alloy.
When my son played at 7 most boys on our team were using -12 or -10, though at 6 several were using -13 or -12.
Thanks baseballready. The last thing Papa looks at is the rule book. Them rule things will get a good baseball team in trouble. Nice question Mr. Brewster.
Been some years ago but I don't remember ever seeing a bat questioned unless it looked like a softball bat. At 7 we had kids using some teeball bats, -13 2 1/4, and some using -8.5 28 inch as 2 5/8. Rec was more particular than the allstars for most parks.