Dlion, there are a lot of young families along 359. Not as many as Fulshear/Katy, but that's because it's smaller and has fewer giant tract home subdivisions.
Texana (which has a good number of Aggie families with young kids) feeds into Frost Elm. It's been a good school for us so far.
As for sports, not sure what you're looking for--
Baseball: that'd be Lamar Little League, which is a big league with a lot of good players
Softball: Rose-Rich--my daughter doesn't play anymore, but the league seems to have plenty of players and parent support
Football: my kid plays flag in an Upwards league at Faith UMC, which is near Texana. There are some other flag leagues around the area and plenty of tackle kids teams
Basketball: my kid also plays in the Upwards league at Faith UMC for this. The Y in Richmond has youth basketball, too.
Volleyball: There are two nearby gyms with volleyball, both club and clinics for younger girls--Texas One on 723 and Catalyst next to Pecan Grove. Daughter has done both, and both are good.
Swimming: Pecan Grove CC has a neighborhood summer team. R&R at the HS natatoria in Rosenberg is another option that's a little more serious.
Gymnastics/Dance: My kids don't do them, but there are a **** ton of them.
Equestrian: again, they're everywhere
Tennis: Pecan Grove CC has lessons and some youth league stuff
As far as other after school activities, you can probably find what you want. Let me know if there's something specific that you're looking for.
Texana's a good kids' neighborhood. Trick or treating there tonight.