A burger is good. A burger with the works is better. The same goes for big-box baby stores. This week downtown Manhattan gets its first such retail oasis, J&R Jr. Occupying the 15,000-square-foot second floor of electronics mecca J&R, the store stocks everything from cribs and car seats to PlayStations and paint sets. The array of gear and goods is vast but selective. And you can shop it all in peace thanks to kiddie diversions throughout the store — think iPads, instruments, art tables, and a baby play yard. Other helpful offerings include baby and birthday registries, citywide messenger service, and free in-store assembly (buy a stroller, walk baby home in it). An on-site event space hosts daily story time and classes by Moonsoup, Rockin’ with Andy, and Little Maestros. And a lineup of monthly family concerts is in the works. We know, it’s a mouthful. J&R Jr., 1 Ann Street, at Broadway (212-238-9060 or jr.com). Photo: Courtesy of J&R Jr. CELEBRATE Valentine’s Day with Rockin’ Railroad What: Experience Kidville’s newest interactive music class with a V-Day themed party. Why: Includes a lovely lunch. When: Tues., 11 a.m.-1 p.m. Where: Kidville, 163 E. 84th St., b/t Third & Lexington Aves. (212-772-8435). Tickets, $35 in advance online at bigcitymoms.com; $40 at the door. GROOVE A Celebration of Black History with Calvin Booker and Friends What: Move your bodies to hip-hop, jazz, and rhythm and blues. Why: Booker channels Savion Glover with his dance style — a mash-up of tap and hip-hop. When: Sat., 1-1:30 p.m. & 2-2:30 p.m. Where: Brooklyn Children’s Museum, 145 Brooklyn Ave., at St. Marks Ave. (718-735-4400). Free with museum admission. TREAT Fastelavn What: The Nordic version of Halloween, where kids dress up in costumes and sing for candy. Why: This Scandinavian sing-along includes games and goodies. When: Sat., 1 p.m. Where: Scandinavia House, 58 Park Ave., at 38th St. Reservations (recommended) to 212-847-9740. Children, $7.