Addition, subtraction and multiplication...OH MY!  
Knowing these facts is an ESSENTIAL part of both third and fourth grade!  If they don't know their facts, they need to practice EVERY SINGLE DAY!  
Here are some ways they can practice at home:
•  Flash Cards
•  Xtramath.org - or other websites!
•  Everyday Math Games
•  Someone quizzing you
•  Fact Triangles
•  Arrays
•  Number Grids

Please help your child learn their facts!  They don't need to spend a lot of time practicing, but it should be something they work on regularly.  Thank you!