Earlybird Kindergarten is meant to be an introduction to beginning math skills. Remember, they are only 5 or 6 years old.
When you get to 1A/1B, you will see it becomes more rigorous. When doing the hands-on math plans HOD has written, you can do as many problems as you like. I often did a handful of problems before moving into the Singapore workbook, which our dc then did quite independently. Children are not meant to have mastered everything introduced in Earlybird Kindergarten. I have really appreciated that Earlybird introduces dc to a lot of different math skills - even things like standard and nonstandard measurement, etc. - rather than only focusing on computation. Many workbook heavy type math programs will have dc complete a ton of problems, but all of the problems are the same. This is redundant IMO, and I have loved having all my bases covered with Singapore's approach of covering all necessary math concepts, but not doing overkill on any one thing. More problems doesn't always mean it's "harder", sometimes it just means more problems 
- with the negative side effect of dc getting careless and making mistakes in the effort to get to the end of the many problems they are assigned. This especially becomes evident in the older grades, where dc using other math programs than Singapore can often be doing math well over an hour a day. This truly is not necessary, and often makes dc dislike math immensely. 
Singapore has fewer problems that are more difficult, often involving several steps to solve. I've learned to love the Singapore way of teaching, but you will know what fits your math style best! In Christ,
Julie