if you want you can just do it at home!! especially since they are close in age & they are getting play dates, so they are getting social skills.
just start setting up a time of at least 2hrs, a day in the morning or afternoon where you turn off the tv, & radio etc. & do learning projects with the kids...they dont have to be anything big, just things like learning the letters of the alphabet, even if they know the alphabet can they recognize the letters in both upper & lower cases? teach them to wrtie the letters...even if your 2yr old isnt quite ready for it all she will enjoy getting to be like big sis. teach them numbers (start in blocks 1-10, then to 20 stc).
work with the calendar & the days of the week, months etc. & the seasons
go to the library & find books that you can read to them
have them paint pictures (use water colors)
at walmart they have books that are geared for each age group, they are workbooks that will give you guidance for things like learning opposites, or matching. they have them for preschool age too.
do shapes & colors
go outside & collect leaves, & flowers & dry them, they can glue them onto paper & make pictures
you will be amazed at how much they learn & also having some structured time will keep their minds working so that they are not left bored & restless just bc you are at home all day.
also there are some good ideas for projects & things to make on sproutonline.com & there are tons of other kid websites to give you ideas.