very nice and demonestrative images .........thanx Emma :)

do you give ms.relaxant after torniquet is on?

you can use a lat.dec.position but what if u elevate the table head or a bit anti-trend. position and manibulation of table can help in controll the level and if u will not let that lateral position for long time, so u will get unilateral block so after block if u turn patient u turn into supine and bit head up and prone when control level and fixation takes place.
Do u use spinal narcotics?

I think it is common trend  where it is bit difficult to cannulate a young child either due to inaccessible veins or fearing of painful prick in case of lacking of EMLA cream. But I think we can do cannulation just after inhalation induction and before intubation to guard against unexpected events.