My oldest daughter hates, HATES having her hair brushed. Whether it was fresh out of the bath or a couple days old, getting her to sit to get her hair brushed was a huge battle. She hates when I try to brush out tangles. So, I decided to look for a solution, and I found it in Johnson's Buddies Easy-Comb Spray.
The product smells great, is easy to apply in the spray bottle, and works great. After washing, you just spray it into wet hair and brush through, and tangles are gone! Or you can spray it into dry hair and it will eliminate tangles that way. It also makes hair soft and seems to help with frizz, too - my daughter has the same light, frizzy hair I have, and it works great at smoothing it (though not quite as well as my grown-up products.) And the bright, kid-friendly packaging got her excited to try it, and now she loves it - she won't let me brush her hair after her baths until I use the spray. It also helps between washes even if you don't spray any more, I've found it can last a couple of days easily before tangles start to reappear. It is also a No More Tears formula, so if you miss while spraying or it drips, you don't have to worry about sore eyes.
If your child has tangle-prone hair, or just hates having it brushes, this could be the solution you need.