I'm not going to get around to much gardening this year sadly as am 38 weeks pregnant and anticipating a low productivity year due to sleep deprivation!
So, I have just bought lots of hardy or true geraniums, I have a couple already and they bush out and provide masses of lovely colour all summer long, very low maintenance. When they finish flowering, you cut them right back and they start all over again! They die back over winter and then should come back every year.
I don't know much about soil types really, most things are done by trial and error in my garden as it feels like the easiest way to learn without getting overwhelmed with science.
I don't spend much on plants in the first place though, so I don't mind if some things don't make it. If anyone in your family or friends circle is interested in gardening, ask their advice as it is invaluable having someone who can actually see the space and what areas you need to fill. Also, they may be able to help with cuttings and some odd plants here and there,I generally try to avoid garden centres as they are expensive. I do swaps with people, buy from my lovely man on the market (the hardy geraniums were £3 which is fine to me, my mum told me off as they are so easy to propagate but I don't have the time or inclination to do that at the moment!) and keep an eye out at plant sales, car boot sales etc where people are getting rid of extra plants they have very cheaply.
I also try mainly to plant perennials which will come back every year. Bedding plants (which will die after the summer) produce a good show of colour but just last for the season so I don't feel they represent good value compared with one's that come back each year.
If you just planting out a raised bed try to plan a bit with height and spread, don't overfill it now. My raised beds are filled with strawberry plants which we got a huge crop from last year, dd absolutely loved picking them! Maybe part of the bed could be fruit or veg and then your toddler could help pick when ready?