for age 3, I'd look for a TOMY "Astro Shooter" as a first machine. small kid friendly size tabletop with actually quite a bit going on.. an upper mid-right flipper, a subway, rollthru's, pop bumpers, kickout holes..
theyre built pretty rugged, very portable, you can make an adapter for 9v RC car pack to take camping etc.

"Atomic Pinball" is the smaller brother of "Astro Shooter" which has much more going for it than atomic. I have a StarCom is same as atomic, a would be battery muncher if I didnt wire in a 5v 700ma power supply. the deepest 1.5v D cell makes the electronic DING, two rows of two D cells (parallel for 3v) runs its single motor that drives everything. very simple to use 1 diode to drop to 3.5v-ish, 3 diodes to drop to 1.5-ish. Astro about 2x the size, 12x20 approximately, runs on a 700ma 9v wall wart. about the only thing Astro doesnt have, is active power slingshots. replacing stock bands with small black scuncii silicone hair ties made the slings REALLY good and bouncy.

true about mechanical flippers (they are), it takes a bit of finger strength for good swats but not horribly. the plus side being no worries about ball holding and burnt coils. in another giant TOY machine, Saitek F1 Formula Challenge (pretty good one btw), I replaced the flipper return pull-springs with lighter-longer ones. TOMY's Astro uses one compression spring between both buttons, is a little stiffer when pushing both simultaneosly.

its a shame zizzle about RAN from producing more, poor flipper button switches failing is issue #1. the TOMY Astro Shooter is a little mechanical marvel, everything running from one little DC motor through levers gears shafts etc. if TOMY had gone a little larger applying the same kind of ingenuity using TWO motors.. lol omg theyed be fun!

another potential candidate might be a Sentinel aka WonderWizard machine (1977-8). they're simplistic "keep the ball alive score points" machines, with both flippers mechanically linked to one solenoid but a pretty easy job to drop in a seperate right flipper mechanism. Sentinels in decent shape sometimes show up in CL for about 100 bucks.
the stock left ball drain is pretty brutal, theres room to add a bounce spring that'll save it about 30% of the time. gameplay IS very simplisticbut they DO slam the ball around fast, good fun with the two little mods just mentioned and very easy to repair if something (solid state) goes out. everything run by single coil solenoids, flippers having an EOS switch that puts a resistor in series to the coil, preventing a burnout. same idea applied to a zizzle might help the flippers be stronger and drop coil voltage when ball holding too, hadnt got around to doing to mine yet to see.