No Expansion Packs Needed:
A*: Master the logic skill and then complete all of the skill challenges of the fishing skill.
A: Master the logic skill and then complete most of the skill challenges of the fishing skill.
A-: Master the logic skill and then complete some of the skill challenges of the fishing skill.
B+: Master the logic skill and then complete one of the skill challenges of the fishing skill.
B: Master the logic skill.
B-: Reach level 9 of the logic skill.
C+: Reach level 8 of the logic skill.
C: Reach level 7 of the logic skill.
C-: Reach level 6 of the logic skill.
D+: Reach level 5 of the logic skill.
D: Reach level 4 of the logic skill.
D-: Reach level 3 of the logic skill.
F: Reach level 2 or less of the logic skill.
A: Master the logic skill and then complete most of the skill challenges of the fishing skill.
A-: Master the logic skill and then complete some of the skill challenges of the fishing skill.
B+: Master the logic skill and then complete one of the skill challenges of the fishing skill.
B: Master the logic skill.
B-: Reach level 9 of the logic skill.
C+: Reach level 8 of the logic skill.
C: Reach level 7 of the logic skill.
C-: Reach level 6 of the logic skill.
D+: Reach level 5 of the logic skill.
D: Reach level 4 of the logic skill.
D-: Reach level 3 of the logic skill.
F: Reach level 2 or less of the logic skill.
Note:
All that your children have to do is learn the first 3 levels of the handiness skill with the building blocks and use the little kids oven to learn the first 3 levels of cooking and learn the logic skill. The two can both be found in the kid's toy's section of buy mode and they look like this... (Though obviously you can change the colour).