Children develop at different rates. This is obvious from an early age. They walk and talk at different times, and school work, including mathematics, is no different. If you are worried about your child's progress, go and talk to their teacher. If the teachers are concerned, they will be able to suggest a number of positive ways forward.
When children don't enjoy maths, it is usually because they are experiencing difficulties and do not understand what they are supposed to do.
Make it practical!
Very often problems arise with young children because they have not had enough practical experience and have been rushed into working with mathematical ideas in the abstract (e.g. sums such as 5 + 1 = 6) before they have had lots of experience of adding real objects together, counting on, knowing that five objects stay the same even if you move them around and knowing that the number 5 is a constant - that it is the same number whether it is cats, dogs, sweets or whatever.
Children need to use practical methods for as long as necessary. If they are given these tools, they will gain in confidence, become competent and eventually discard them. If they are pushed into the abstract world of maths too soon, they will not understand and become confused.
When something is demonstrated using counters, number lines, real objects related to a story (e.g. three bears), your child will begin to see the connection between the numbers and the objects.
Even when children are older, and are comfortable with abstract maths in lots of situations, it is always worth trying going back to representing the maths using objects or pictures, to help them make the connection to the abstract.
Try to make it fun and relevant
Children will enjoy maths more if it is presented in a fun and relevant way. If they need to be motivated, play games with them and let them experience success. Use any opportunity (cooking, shopping, planting in the garden) as an opportunity to develop your child's number skills - but try to keep it fun and act enthusiastic. Maths is everywhere and as children start to use it to make sense of their world and recognise its relevance, they tend to enjoy it more.
Take it slow and easy
If your child wants to work at an easier level or a slower pace, go along with this. Make 'sums' easy - do not progress to higher numbers until they are totally confident and have had lots of hands-on, practical experience. Learning to be good at maths takes time and patience. Maths is nothing more than building from one stage to the next. The foundations must be secure. Whenever you do maths work with your child, make sure it's in a relaxed and comfortable environment, and praise their efforts.
Keep playing games
Play lots of maths games and show that you enjoy the activities. Try board games, playing cards, dice and dominoes. Make it easy so that your child experiences success over and over again, and gains confidence.