My advice would be to do and prepare your own food and stay clear of highly processed food, even healthy type.
Bake your own seeds crackers it is so easy www.bite.co.nz/recipe/11727/Seed-crackers-gluten-and-dairy-free/ or www.taste.com.au/recipes/healthy-seed-crackers/e5e63200-85da-4b2a-9437-3da0e3c43f46 .
Or your own bread , crepes here a vegan gluten free minimalistbaker.com/5-ingredient-buckwheat-crepes/
Chickpea flour is great for zucchini muffin. There are so many vegan website for recipes without eggs and dairy.
Try to boil the fish instead of putting a batter and fry it (cod filets are nice boiled) and put a bit of olive oil and a sprinkle of parsley on top. Avoid processed meat and just put a good quality steak in a pan with olive oil, rosemary and crystal salt.
It is a vicious circle. You lack, good bacteria , your immune system is weaker, you get more infection, you receive more antibiotics and you are back to square one and it only gets worse and worse.
I have an important piece of advice concerning pro and pre biotics. You can swallow as many pills as you like but if you don;t change the diet, those bacteria will die in no time and no change will last. Take the probiotics, preferably home made, you get far more species, and then you MUST feed those bacteria. Rolled oats, green bananas, cold rice and cold pasta, the green bit of the leeks (roasted in oven is one of the nicest thing to eat, every guest in my house goes banana over it : buy whole leeks, not just the white part, Wash and cut into stripes, dry in a tea towel, put in a big bowl, add olive oil, a bit of smoked paprika or smoke liquid, mixed herbs, crystal salt and mix with your hand. Put in an oven tray in a thin layer, each stripe separated from the other and bake in the oven and repeat until all cooked) , every kind of green with strong fibre.
Do some seaweed crackers by roasting the inexpensive nori sheets from the Asian section at supermarket. I do them more or less this way super quick, easy and cheap but your kitchen will stink!
Add onions, garlic to your dishes and be generous with fresh herbs. For snacks, let him have blueberries, apple and pear with the peel.
Without the diet, you have just wasted money on probiotics. It is like planting seeds in your garden and then putting a big black plastic sheet on top and never adding water or allowing sunshine. . Nothing will grow. Even if you add fertiliser .
You don't need big quantities. One tablespoon a day of any probiotic food is enough and not even every day and double that for the probiotics food. And then a nice mediterranean diet for the whole family.
Some companies can analyse the DNA of the species you have and it gives your an idea of the health of your gut. in UK, you can get a list for 75 pounds with them britishgut.org/faq/ they won't tell you if it bad or good, You will receive a bacterial profile of your sample and a general overview of how your profile compares to that of others in the project. What we are not able provide is medical advice, such as how you should change your diet or what microbes you might be lacking. We are ethically and legally prohibited from giving such advice as a research laboratory " but you can find out that yourself or enrol the help of a naturopath or dietician who specialised in gut health..
Like everything in the medical world, there is a gap between research and discoveries and change in medical protocol. but with internet the access to knowledge is infinite and if you stick to medical papers, your research is valid. Pubmed is a good starting point
But you don;t want to start playing the witch doctor and for that reason, sticking to food and not pills is a safe choice. There is still so much we don't know about the bacteria species and you can do harm by overdoing, especially in a toddler or baby. There are many books on the gut, read them, but caution.
A tiny piece of roquefort (sheep milk) has millions of bacteria. A miso soup ditto. Food that existed 100 years ago and that you can reproduce in your kitchen without an engineering degree.
There is no way I can transform corn kernels into a doritos, no matter how long I try.
As my last word, I repeat CAUTION.