Can anyone suggest a good first grade science project for a homeschool family?

My oldest is a homeschooled 1st grader and she is getting burned out. I'd like to do some kind of age-appropriate science project that won't take forever or make a horrible mess, tall order I know that's why I'm asking for help! We are getting close to being done with her work for the year, but she's ready to be done for the year and I thought something like this might help improve her attitude. Ideally, this would be a project that her 5 year old preschool brother could participate in as well, he hates being left out.

I'm also open to other general suggestions on getting her motivated for this last little bit. I know a big part of her problem is that she's really doing things that are primarily review. She is honing her basic math skills and really needs the practice, but she's not really getting into new things right now. She also reads well above grade level, but we feel it's important for her to have a good grasp of the basics in the core areas, even if her books are written below her reading level. She also has benefited from the material as it has reinforced the need to read carefully rather than guessing. For these reasons I really want to get her through the textbooks we have been using.

I basically used more of an unschooling approach last year for Kindergarten, but it left some gaps I wasn't happy about. We enrolled her at the beginning of this year at our local school, but had a number of problems with it and took her out after about a month. She loves homeschool and regularly says how much better it is than when she was in school, but in that short month she went from begging me for more schoolwork constantly to fighting having to do any schoolwork. She has improved some, but we are back to really struggling like we were with homework and when we first went back to homeschooling. Another mark against us, the area homeschool groups are really winding down right now so we don't have the opportunity for some of the activities she really enjoys right now.

I'd love some ideas from other homeschoolers to get us through this final stretch.