Everyone here will say the most accurate way of reading your spa is the Taylor test kits (K-2006.)
Personally, I use test strips because they are accurate enough, and I am lazy.
Don't bother with electronic strip meters. In my experience, they are all over the place. Unless you are paying a lot of money for one, the $70-$100 electronic meters give you a different reading every time.
I test once a week, which is what I would recommend for anyone.
Finally, I have a 2.5 year old son who will join me from time to time. Little ones can't dissipate heat as well as we can. Make sure they are well hydrated and that the temp isn't to high (102 max is what I would recommend.)
My son sweats to high heaven, so he is a tolerant of the heat for long periods of time. Just make sure you make them drink plenty of water.
If they are less than a year old, I wouldn't really have them in your hot tub for more than 10-15 minutes. Just my 2 cents.