Every new instrument has a learning curve, however the trombone is somewhat unique in its requirements. Smaller players may find this difficult to hold and manoeuvre and some positions on the slide may not be reachable for a very young child. There is also the added consideration of strength, as repeated extension of the arm and the muscle control required for the positions can be hard for new players. If this is the first brass instrument, a new player would also need to train their facial muscles so that they can achieve and vary their embouchure (the position their mouth should be in to play). Trombone sheet music can also be written in several clefs, which can be an added challenge for some learners.
There are, however, benefits to learning the trombone! The slide position positioning can be more intuitive than the pistons on other brass instruments as these are sequential. It is also easier to achieve a noise initially due to the larger mouthpiece. As with any instrument, learning the trombone has its benefits - the important thing is to practise. We would also recommend finding a teacher to avoid falling into any bad habits that could affect your playing.