Your children may be tired too.
Making it a habit to do schoolwork together is important. Adding to the curriculum is even more important. In an education system where less than 10% of science classrooms perform experiments with their students, it is your job as a parent to take the weight.
I am an advocate of educating your own children. Honestly, I don't know when it happened, but parents have shrugged off teaching life skills and academics to their children. I hear parents say, "It's the school's job, not mine...” That is just not true.
Every day you should pick something to do with your child that involves thinking and doing. For example, maybe you will go out, collect leaves from plants, and research the plants using a flora and fauna book.