Remember it's not just about avoiding sunburn. UVA also causes skin damage and you can take up to 1000 times more UVA than UVB before burning.
High SPF and a sunscreen with both UVA and UVB protection are essential especially for young children.
Don't rub your sunscreen in vigorously. For best results apply a two layers - a layer of moisturiser and then a layer of sunscreen only lightly rubbed in. If children go swimming, make sure that sunscreen is reapplied.
If possible, stay in the shade between 11am and 3pm - take children somewhere shaded for lunch.
Try to cover up with a hat, t-shirt and sunglasses - a sunhat and t-shirt for children are a must. Babies need adequate protection, including a sunshade on the pram.