To folks traveling with young children-- GOOD FOR YOU!
My first visit to "this side" was in 2004 with my 4 kids (12, 15, 17, 19). The drug seen was evident, but not pushy. In fact, funny story, one of the notorious drug dealers of the day actually cautioned me that my youngest had been looking at a pipe. Seriously. I had met him earlier in the day, told him i didn't want to buy anything, gave him "a red" (a mil colones= $2) and a quart of milk to watch my car, and asked him not to harass me or my kids. Later that night, my kids are looking at the booths, i'm in a restaurant across the street. I go to check on my kids and he pulls me aside sayin'... "don't worry momma, i won't sell your kids no trouble". My son later explained the same situation, but his version was he didn't know it was a pipe and was attracted to the gecko carved into it.
Nearly 10 years later, not a whole lot has changed in that way. If you want drugs, you will likely find them. If you don't, (and I suggest you don't), be straight up and tell them you're not interested. This place is NOT like Cancun, Ixtapa, Puerto Vallarta where you're constantly shook down by dealers, vendors, beggars or all the above.
We do have our local panhandlers (weird word), there are about a handful of them who will stop you at the market or offer to watch your car while you dine. I've decided against giving money, and have told them that, for the most part. But, when they watch my car, carry my groceries, clean up beach litter, recycle bottles, whatever, I'm quick to reward them with a loaf of bread, cold juice, or hygiene item they ask for.
Most of the vendors approaching you on the beach (and there aren't many, but 1-2 during a busy weekend) are foreigners trying to make it here selling baked goods or jewelry. I sometimes wish the pipa fria vendors (water coconuts) were more industrious... as there is nothing like a cold pipa on a hot beach!
I think you and your kids will have a great time. I think you will have some great teachable moments to share with your kids about living simply, making good choices, being active, respecting the earth and honoring diversity of all people.
Let us know how it goes, please.