Daisy,
I agree with you that math should not be taking that long every day and that while some of it may be due to issues of maturity or diligence, at least part of the problem is the sheer volume of problems in the daily assignments that you mentioned. Overkill on drill (or supersizing everything) is something that we do too much of here in the U.S.! We always seem to think more is better and sometimes more is just... more.
This is one of the big reasons that Singapore appeals to me. It is more Charlotte-Mason in that it contains fewer problems that require a higher level of thinking. Yes, it is hard work sometimes to think through some of the problems, but since there aren't pages of problems we're more willing to persevere, and I'm more willing to help (as I can see the end of the assignment not far away).
Additional drill and practice is one of the easiest things to add to any math program. Higher-level thinking, mental math, and reasoning are harder to add to a program. While you can always add in a workbook that contains higher level problems, it often doesn't sink in as well as if the whole program was using the methods of training kiddos "how to think to find the answers".
No math program is a perfect fit for everyone, but we've found the combination of short lessons with fewer problems of a higher level to be a winner here.
I'd start your son where he placed and start your daughter one book back (just to help her gain some confidence). Be warned that the 'A' books of each level are harder at the beginning and then even out as the book progresses. So, if you need to slow down at the start to be successful do it. Also, don't worry about mastery each day, just keep moving forward steadily progressing. The concepts will come up again. We've never slowed down to do extra practice. If the kiddos need extra help, I sit beside them and talk through it with them, but we keep moving forward. Not everything is meant to be mastered in its first introduction. Singapore is a layered approach.
Last, I wouldn't hurry too fast through the levels or you'll quickly get to a level that is too difficult too soon. If it feels easy in parts, celebrate that! We have found that Singapore has a good ebb and flow of hard concepts and then easier ones. However, if too much additional drill and practice is added then you'll lose the ebb and flow it will feel like the kiddos are in the hard concepts all of the time.
My second son is just starting 4A now, and he is a mathy kiddo. He always scores in the 99th percentile in math on his standardized tests, yet he's just beginning 4A in the last 3 months of grade 4. He's right where he should be and enjoys his math lessons. I share this to let you know not to worry about rushing.
When feeling the desire to rush, ask yourself, "Where are we rushing to get to?" If its the higher level concepts, then with Singapore you'll already have that earlier than in most other programs. The thinking is built into the lessons so that kiddos excel even a book or two behind when compared to the scope and sequence of other programs.
Blessings,
Carrie
while we finish Beyond for this year. It's one book lower for each than they might have been placed at, but this way they get some review, fill in any gaps, we see how it works, and I have Carrie's activities for each.