T.G.
I bought a sit n stand when I was pregnant with my 3rd and had a 6 and a 9 year old. Our 6 year old has leg issues so she often needs to sit more than most kids. I loved it. It was awesome and my daughter did great in it. I actually ended up watching a second baby and needed a double stroller for the 2 babies. I bought a side by side which was a pain and my 6 year old didn't really sit in it well. So we didn't use it too often. We sold the sit n stand to buy the double and I miss the sit n stand SO MUCH!!! I just don't want to spend the money again.
Now my baby is 1 1/2 and I have a Peg Perego which has this thing in the back it seems so a bigger kid can stand on? Maybe that is not what it is for, but we use it for that. My 7 year old stands there great and it's awesome. But now that my little one walks well sometimes we will let my 7 year old sit and the little one walk. But I still think sometimes I would love a sit n stand again. Worth every penny! Go for it!! Especially because your kids are so much younger. We bought the cheaper Baby Trend one at Target and I LOVED it.