I think, realistically, you need to make the time for your dog. I totally understand that it is hard juggling the needs of children and dogs - I have a 2 young children and a 5yr old dog (who has always been rather on the complex side as far as training needs go!).
But, at the end of the day, all responsibilities were acquired by our choice, so it's up to me/us to ensure all get their needs met. Yes, training has diminished over the past 7 months, but we do not do child activities unless there is a plan in place to meet the needs of the dog. This means we don't join morning groups, so we can walk the dog, before going out to child activities in the afternoon. If weather is poor, we simply put on waterproofs... If it is horrendous, or a child is too ill, I ensure the dog gets 30mins training throughout the day. It can be very difficult, and I really *should* do more, but it really does help.
We have ensured that Honey has a reasonably solid "leave it" command, so food held by my toddler is generally safe, but she will steal any food left lying around... so it's down to me to make sure she doesn't get the opportunity (and, in time, my children, to learn not to put food down if they want it back!!!!). She can be very whiny when she is excited, and getting myself, 2 children and a dog ready for a walk does tend to result in very annoying whining... but generally a couple of simple commands "Sit" "down" etc, with rewards, resets her mute button for a while!!! Fortunately she's not particularly whiney in the car - we spent a long time when she was a pup handfeeding her in the car - but she has adapted very well to changing from travelling on a passenger seat (with dog seat-belt) to crate in the boot - so a change of travelling position may help - it's worth giving it a try.
At 3.5, your toddler is old enough to be involved in some basic training (even just passing you treats at first), which can make it easier to find the time for some fun short-bursts of training, and will help to integrate your dog into your family dynamic.
I hope you don't think I am being too harsh in what I am saying - I really do understand how hard it can be to continue to make adaquate time for a dog, but I really think if you are able to, you (and he) will be much happier - and it will model proper responsible pet ownership for your son.
