I bought my daughter (2.9) and stepson (10) UV protection t-shirts as they have very pale, delicate skin. I got them in France, at Decathlon, for peanuts (a few euros each) in quite nice colours, and they wear them to death in the sun and when swimming outdoors.
Sunscreens have improved hugely but there are emerging issues with them producing free radicals (ie they cause cancer) and it really is preferable to cover children up with t-shirts and hats and keep them in the shade as much as possible. And that way you avoid the irritation issues.