I personally don't think you should get rid of the guinea pig because you can use him/her as a learning tool to teach your child responsibility. As for the smell.
I clean my guinea pigs cage once a week (and spot clean every morning but that isn't necessary). When I clean his cage, I will obviously throw away the previous weeks bedding (or you can put it in the compost if you do the whole compost thing), then I scrub down his cage with just regular dish soap and hot water and scrub it down really well with a harsh sponge or something to make sure I got all the residue off from the poop and such. Then when I rinse that off and dry it off, I use super pet clean cage safe deodorizer and clean it off again. Then I’ll sprinkle some baking soda on the bottom of the cage (Yes, it is safe for guinea pigs. We put it in our fridges, we eat baking soda, we clean with baking soda and it’s fine to use for guinea pigs). Then I’ll put the bedding over that. Then put all of his toys, water and food back in his cage and put my guinea pig back in the cage. In the mornings before I leave for school or work, I’ll spray a little bit of “nature’s miracle cage Oder eliminator for small animals” while I let Herman run around and play. Also, if you feel the need to, sprinkle a tiny bit of baking soda as well and just mix it up. I know it seems like allot but I promise you, even though it still smells at the end of the week, it’s not as bad as if you did nothing. It helps soooooooooo much. I have tried carefresh bedding but I have found it doesn’t work too well and it makes it so much harder to clean and it’s allot messier. I used to have the same problem with his cage stinking after three days as well, but if you follow this, it won’t be as bad, usually day 5/6 smells like what day 3/4 would normally smell like.
I’m also a candle addict and I use an air cleaner. So that helps too. I also open the windows when the weather is nice.
Also, you really shouldn’t give them a bath more than once a month. It’s bad for their skin. I hope this helps!