Here are some of the websites and resources which children use to develop their maths skills.
Numbots - Daily practice for KS1 pupils to help with number (subitising; Number Bonds; Addition & Subtraction)
Hit the Button An interactive maths game with quick fire questions on number bonds, times tables, doubling and halving, multiples, division facts and square numbers. The games are against the clock to challenge and develop a child’s mental maths skills.  
Times table Quizzes
Maths is Fun Interactive puzzles, quizzes and games 
Times Tables Rockstars Interactive games for practicing times tables 
Hegarty Maths Online maths work, for year 6 only