The research involved 10 children, some of whom had iPads while others played with toys.
Prof Straker said those who used iPads moved their upper limbs and whole body less in a 15 minute period than when they played with toys, but more than when they watched TV.
The results showed children playing with toys moved their upper limbs six times as much as when watching TV and three times as much as when using an iPad.
Children playing with toys also moved their whole body twice as much compared to when using an iPad and three times more than watching TV.
Prof Straker said: ‘We are concerned that the very enticing touch screen devices will lead to children’s muscles and bones not developing well for two reasons.