Some of my favourite worksheets of recent times have just been published for Year 1. They provide rich problem solving activities for those who have mastered the basic addition and subtraction skills. The shopping and money worksheets are bright and colourful as well as having little writing, but they really pack a punch when it comes to mathematical thinking.
A key aspect of the mastery approach to maths is that children have to describe problems in their own words and explain how solutions are reached. All the questions need careful thought but the later sets (2 and 3) require two steps to reach the answer. As well as looking at the working out, it is well worth asking your child how they go about getting the answer and why they are doing what they are doing.