I think it's a good idea that each year you toss out the old stuff and bring in the new stuff, I'm talking sunscreens that is (my husband would like me to think of EVERYTHING in this way, but if I did I would toss him out! ha, just kidding!) maybe two years, tops! Depending on where you live, sunscreen might be a year round thing for you in which case this is no problem. But check dates on the package and see when they expire, and if it's in questions, toss it!
This year the Environmental Working Group (EWG) updated it's top sunscreens as they do each year and for me, I think that the list of okay products is growing, which is such good news! In this house we like to use Vivesana, I think it's a great product, and much like the old Dr. Hauschka sunscreens (no longer sold here in the USA) you can put it on in the morning and it does a pretty good job of sticking around most of the day unless you are at the beach from morning until night, in which case I would apply twice.
I think that the best option for kids is hats and cotton clothing to block the harmful sun rays instead of using sunscreen each and every day but you need to be the judge of that, and it varies where you live. Take a look at the EWG list of top sunscreens and make sure yours is a good one! (otherwise toss it!)
click here to see the EWG sunscreen list
click here to look up your sunscreen and see how it rates
see previous posts on sunscreens here