These sites have an excellent range of activities and games for most topics. Top Marks, Cool Maths, Maths is Fun, SUMS Maths are particularly good as also give explanations. BBC has good video clips.
Top Marks
Age 5-7
https://www.topmarks.co.uk/maths-games/5-7-years/counting
Age 7-11
https://www.topmarks.co.uk/maths-games/7-11-years/ordering-and-sequencing-numbers
Cool Maths 4 Kids – also includes lessons/explanations/brain teasers
http://www.coolmath4kids.com/
Maths is fun
Range of explanations and online activities
https://www.mathsisfun.com/numbers/index.html
SUMS Maths
Mostly aimed at KS2 (go to Easy and Easy 2 for Early Years and KS1). Games sorted into: Number, Data Handling, Calculations, Shape and Space. Well-supported with explanations as children play the game and solve the questions
http://www.sums.co.uk/original/
BBC Bitesize
KS1 and KS2 clips to help explain strategies, simply explained in a fun way to engage children
http://www.bbc.co.uk/education
Activities for KS1 no longer being updated
http://www.bbc.co.uk/bitesize/ks1/maths/
Arcademics Skill Builders – games to play against the computer or a friend
http://www.arcademics.com/
Woodland Junior School
http://resources.woodlands-junior.kent.sch.uk/maths/