I put my kids on SRAM triggers straight away, the front mech can still be stiff though especially on upshift, couple of other things to try;
Rotate the shifter so they can get more thumb leverage on the lever, pushing down rather than through is easier for small hands.
Also it’s not all about the shifters – most front mechs have a lot of spring tension. They are not really adjustable but you can bend them, though it can then make the downshift less reliable as it might to derail the chain, though I’ve found the old SRAM 7.0 front mech the spring location / design is such they are much, much easier to shift. You can still get them £10 on ebay.