This is a quick and easy pattern for a child's pullover sweater, made in one piece.  This style has a boat neck and 3/4 length sleeves.  It's called the "Oxfam Sweater" because I learned about this sweater being used by the international aid agency Oxfam.  Here's a link to an article about it:    Knitting Sweaters to Help Children

I translated the knitting pattern in the article into measurements in inches.  This allows you to use any size hook and yarn, not worry about gauge, yet still make the sweater a standard size. :

Use any size crochet hook and any size yarn.  All instructions are given in inches, so you will need to measure each critical dimension, rather than counting stitches.  I have written these instructions using single crochet as the pattern stitch, but you may use any pattern stitch as long as the measurements work out.  Just for reference, I made this sweater in size 4, using an H hook, and it took 10 oz. of Red Heart yarn.

NOTE:  If your crocheting tends to "expand" slightly as you work up from the foundation chain, work your starting chains slightly shorter than your desired finished length. 

Foundation Chain:   Chain until your chain is the length of the Body Width. 

Front Body:  Chain one and turn.  Single crochet back along the chain.  Repeat this row until piece measures the length of the Body Length.

Add first sleeve:  Chain until chain measures the length of the Sleeve Length.  Chain one and turn.  Single crochet back along the chain and across the sweater body.

Add second sleeve:  Chain until chain measures the length of the Sleeve Length.  Chain one and turn.  Single crochet back along the chain and across the sweater body and other sleeve.

Front Sleeves:  Chain one and turn.  Single crochet across.  Repeat until length from beginning of sleeve rows measures the length of the Sleeve Width.

First Neck Opening Row:  Chain one and turn.  Crochet back the length of Length X.  Chain until the length of the chain measures the length of the Neck Opening.  Measure this same distance along the sweater body from the last single crochet you worked.  Begin single crocheting again at the measured distance and continue across the piece to the end of the sleeve.  This forms the gap for the neck opening.

Second Neck Opening Row:  Chain one and turn.  Single crochet back along the sleeve, chains, and other sleeve.

Back Sleeves:  Repeat the Front Sleeve rows as above, adding the same number of rows.  When you fold the sleeves along the midline, parallel to the neck opening, both the front and back of the sleeves should be the same width as the Sleeve Width measurement.

Back Body:  Chain one and turn.  Single crochet the length of the Sleeve Length plus the Body Width.  Chain one and turn.  Single crochet the Body Width.  Chain one and turn.  Continue working this piece until measurement from sleeves matches the Body Length measurement.

Finishing:  Finish off.  Sew underarm seams by sewing along the sleeve length and body length.  Weave in all ends.

Edging:  Work the edging of your choice around the neck opening, sleeves, and waist.  Weave in ends.  My favorite edging is the reverse single crochet.  Work it as follows:  single crochet from Left to Right -- backwards from the normal direction.  It's a bit awkward at first, but work slowly and I think you'll be pleased with the resulting rolled finish.