With so many activities free in September, families can keep an eye on their budgets and still find plenty of things to do in Boston with kids. This month, Museum Day lets visitors get free admission to participating locations all over Massachusetts. Curious kids can touch a truck or even explore a plane. And September in Boston has free fairs and festivals all month long, including Riverfest in Somerville, the South Boston Street Festival, and the Boston Local Food Festival. Given all these free things to do in Boston in September, there’s every reason to get out and have fun with the family! So read on for our picks for the top things to do in Boston with kids that are free in September.