Division requires following a certain procedure, just as multiplication by multiple digits does. But you want to be sure that your child understands why the procedures that we use in division are followed because then he/she is more likely to remember how to do this type of problem. For this example: 42 divided by 3, follow this procedure.
First, ask your child to count out 42 items. Pennies are particularly convenient to use; provide some small bags or envelopes to put them in. Once the 42 items are counted out, ask your child to group them in hundreds until there aren’t 100 left to group, then in tens until there aren’t ten to group, and to keep the rest out as “ones”. The grouped items can be placed in the envelopes or just stacked as this problem doesn’t require a large number of manipulatives.
Now, since the items will be divided into 3 groups, ask your child to divide up the largest group first. There won’t be any items in the hundreds stack, so your child’s attention should go to the 4 stacks/envelopes that make up the tens groups. Set 3 mats (pieces of paper are fine) out, since the problem asks that the items be divided into 3 groups and invite your child to divide the tens stacks. At this point he/she may NOT break a stack to divide it; only groups of ten may be divided. When finished, your child should find that there is one stack of ten on each mat, that there is one stack of ten that couldn’t be divided (since it can’t be split just yet) and there are those 2 loose items over in the ones pile.
Since the tens stack that remains couldn’t be divided into three, invite your child to open the stack and spread out the 10 pennies. Ask, “separated out like this, what does each penny stand for?” It can’t stand for 10 any longer; that group was broken up. Yes, each one is a “one” just like those 2 loose ones. If they are all ones, then they may be grouped together and then with the 12 ones available, your child should divide those onto the 3 mats. Each mat now has one stack of 10 and 4 loose ones. Remembering what you know about expanded notation, your 10 + 4 is the same thing as 14. You have divided 42 items into 3 groups and each group has 14 items.