Hi and welcome Sue, let us help you with one one ore two issues with your surfing.
Let's start with the easiest to fix, you will never beat your teenage sons in learning to surf unless you break their legs for a number of years
They are teenagers and at the peak of their physical learning skills, it would be the same for a teenage daughter, so forget that misconception of beating your children (at surfing) immediately !
FIXED.
Now about the nose diving : this something all surfers have to overcome and the cause varies from wave to wave for different reasons.
Are you at just catching the white water stage?
Are your riding a long or a short board?
Do you let the wave catch you or do you catch it?
Do you have your legs together or apart

Impertinent but pertinent to wave catching!
What is your assessment of the waves where you surf?
In this there is an answer!
We can work on your stuff from there
