I need to raise the height of my handle bars.

I am not sure which question to answer, so I will try both.

raising the handlebars, loosen the stem bolt 4or 5 turns, (this is the bolt on on the top of the handlebar stem). Tap the stem bolt with a hammer, the bold should drop down and the handle bars should fall loose, adjust as needed, then tighten the stem bolt to set.
Please note, there is usually a limit line on the stem, do not raise bars above this level as iy will make the handle bars unsafe and could pull out or break off.

second question, Child seats ar very adaptable, an will fit most bikes. Be sure to use all the necessary hard ware and safety guards. for you and your passenger.
Try to get the seat set up as low as possible as the higher the seat the higher the center of gravity. It will have less effect on handling characteristics if you keep the seat low.

I hope this is of some help.
Ed