If you're at all considering it I would use it - their skin is so sensitive it's better to be safe than sorry. Although I only used it if they had shorts or a t-shirt on - very rarely on just their face iykwim!
get some lotion made for babies, I use soltan on ds, seems pretty good. He hasn't got burnt, or even pink, and it hasn't bothered his skin even though he's usually really sensitive to lotions and creams. you can get burnt even when it's not sunny so I put suncream on ds everyday if he's going to be outside.